Added prefer_type_checking rule

[mildm8nnered]

I wrote this unaware of #5561

I think that PR should take precedence over this one, but I'm just leaving this here in case @ikelax wants to steal anything from it.

[SwiftLintBot]

	27 Warnings
⚠️	If this is a user-facing change, please include a CHANGELOG entry to credit yourself! You can find it at CHANGELOG.md.
⚠️	This PR introduced a violation in Firefox: /firefox-ios/Client/Frontend/Browser/BrowserViewController/Views/BrowserViewController.swift:2233:81: warning: Prefer Type Checking Violation: Prefer a is X to a as? X != nil (prefer_type_checking)
⚠️	This PR introduced a violation in Firefox: /firefox-ios/Client/Frontend/Browser/BrowserViewController/Views/BrowserViewController.swift:448:41: warning: Prefer Type Checking Violation: Prefer a is X to a as? X != nil (prefer_type_checking)
⚠️	This PR introduced a violation in Firefox: /firefox-ios/Client/Frontend/Browser/BrowserViewController/Views/BrowserViewController.swift:459:41: warning: Prefer Type Checking Violation: Prefer a is X to a as? X != nil (prefer_type_checking)
⚠️	This PR introduced a violation in Firefox: /firefox-ios/Client/Frontend/Browser/TabDisplayManager.swift:457:46: warning: Prefer Type Checking Violation: Prefer a is X to a as? X != nil (prefer_type_checking)
⚠️	This PR introduced a violation in Firefox: /firefox-ios/Client/Frontend/Browser/TabDisplayManager.swift:700:29: warning: Prefer Type Checking Violation: Prefer a is X to a as? X != nil (prefer_type_checking)
⚠️	This PR introduced a violation in Firefox: /firefox-ios/Client/Frontend/Home/HomepageContextMenuHelper.swift:271:24: warning: Prefer Type Checking Violation: Prefer a is X to a as? X != nil (prefer_type_checking)
⚠️	This PR introduced a violation in Firefox: /firefox-ios/Client/Frontend/Home/HomepageViewController.swift:325:36: warning: Prefer Type Checking Violation: Prefer a is X to a as? X != nil (prefer_type_checking)
⚠️	This PR introduced a violation in Firefox: /firefox-ios/Client/Frontend/Home/TopSites/DataManagement/TopSitesDataAdaptor.swift:183:19: warning: Prefer Type Checking Violation: Prefer a is X to a as? X != nil (prefer_type_checking)
⚠️	This PR introduced a violation in Firefox: /firefox-ios/Client/Frontend/Library/HistoryPanel/HistoryPanel.swift:548:17: warning: Prefer Type Checking Violation: Prefer a is X to a as? X != nil (prefer_type_checking)
⚠️	This PR introduced a violation in Firefox: /firefox-ios/Client/Frontend/Settings/SettingsTableViewController.swift:1012:20: warning: Prefer Type Checking Violation: Prefer a is X to a as? X != nil (prefer_type_checking)
⚠️	This PR introduced a violation in Firefox: /firefox-ios/Client/Frontend/TabContentsScripts/LoginsHelper.swift:326:35: warning: Prefer Type Checking Violation: Prefer a is X to a as? X != nil (prefer_type_checking)
⚠️	This PR introduced a violation in Firefox: /firefox-ios/Client/Frontend/TabContentsScripts/LoginsHelper.swift:327:37: warning: Prefer Type Checking Violation: Prefer a is X to a as? X != nil (prefer_type_checking)
⚠️	This PR introduced a violation in Firefox: /firefox-ios/Client/Frontend/Widgets/SiteTableViewController.swift:112:41: warning: Prefer Type Checking Violation: Prefer a is X to a as? X != nil (prefer_type_checking)
⚠️	This PR introduced a violation in Firefox: /firefox-ios/Client/Frontend/Widgets/SiteTableViewController.swift:54:17: warning: Prefer Type Checking Violation: Prefer a is X to a as? X != nil (prefer_type_checking)
⚠️	This PR introduced a violation in Kickstarter: /Library/TestHelpers/MockStripeIntentService.swift:18:41: warning: Prefer Type Checking Violation: Prefer a is X to a as? X != nil (prefer_type_checking)
⚠️	This PR introduced a violation in Kickstarter: /Library/TestHelpers/MockStripeIntentService.swift:39:41: warning: Prefer Type Checking Violation: Prefer a is X to a as? X != nil (prefer_type_checking)
⚠️	This PR introduced a violation in Nimble: /Sources/Nimble/Matchers/MatchError.swift:62:24: warning: Prefer Type Checking Violation: Prefer a is X to a as? X != nil (prefer_type_checking)
⚠️	This PR introduced a violation in Realm: /RealmSwift/Impl/SchemaDiscovery.swift:157:27: warning: Prefer Type Checking Violation: Prefer a is X to a as? X != nil (prefer_type_checking)
⚠️	This PR introduced a violation in Realm: /RealmSwift/Realm.swift:1375:30: warning: Prefer Type Checking Violation: Prefer a is X to a as? X != nil (prefer_type_checking)
⚠️	This PR introduced a violation in Sourcery: /SourceryTests/Stub/Performance-Code/Kiosk/App/AppViewController.swift:79:36: warning: Prefer Type Checking Violation: Prefer a is X to a as? X != nil (prefer_type_checking)
⚠️	This PR introduced a violation in Swift: /stdlib/public/core/BridgeObjectiveC.swift:819:25: warning: Prefer Type Checking Violation: Prefer a is X to a as? X != nil (prefer_type_checking)
⚠️	This PR introduced a violation in Wire: /wire-ios-request-strategy/Tests/Sources/Payloads/Processing/ConversationEventPayloadProcessorTests.swift:1375:76: warning: Prefer Type Checking Violation: Prefer a is X to a as? X != nil (prefer_type_checking)
⚠️	This PR introduced a violation in Wire: /wire-ios/Wire-iOS/Sources/UserInterface/Components/Views/MarkdownTextView+Recognizers.swift:41:61: warning: Prefer Type Checking Violation: Prefer a is X to a as? X != nil (prefer_type_checking)
⚠️	This PR introduced a violation in WordPress: /WordPress/Classes/ViewRelated/Blog/My Site/MySiteViewController.swift:788:52: warning: Prefer Type Checking Violation: Prefer a is X to a as? X != nil (prefer_type_checking)
⚠️	This PR introduced a violation in WordPress: /WordPress/Classes/ViewRelated/Notifications/Tools/NotificationMediaDownloader.swift:98:88: warning: Prefer Type Checking Violation: Prefer a is X to a as? X != nil (prefer_type_checking)
⚠️	This PR introduced a violation in WordPress: /WordPress/Classes/ViewRelated/Reader/ReaderCardsStreamViewController.swift:256:18: warning: Prefer Type Checking Violation: Prefer a is X to a as? X != nil (prefer_type_checking)

	17 Messages
📖	Linting Aerial with this PR took 0.69s vs 0.67s on main (2% slower)
📖	Linting Alamofire with this PR took 0.92s vs 0.94s on main (2% faster)
📖	Linting Brave with this PR took 5.27s vs 5.31s on main (0% faster)
📖	Linting DuckDuckGo with this PR took 3.01s vs 3.04s on main (0% faster)
📖	Linting Firefox with this PR took 8.17s vs 8.12s on main (0% slower)
📖	Linting Kickstarter with this PR took 6.87s vs 6.87s on main (0% slower)
📖	Linting Moya with this PR took 0.42s vs 0.42s on main (0% slower)
📖	Linting NetNewsWire with this PR took 1.88s vs 1.83s on main (2% slower)
📖	Linting Nimble with this PR took 0.58s vs 0.57s on main (1% slower)
📖	Linting PocketCasts with this PR took 6.17s vs 6.21s on main (0% faster)
📖	Linting Quick with this PR took 0.34s vs 0.35s on main (2% faster)
📖	Linting Realm with this PR took 3.46s vs 3.43s on main (0% slower)
📖	Linting Sourcery with this PR took 1.75s vs 1.79s on main (2% faster)
📖	Linting Swift with this PR took 3.2s vs 3.15s on main (1% slower)
📖	Linting VLC with this PR took 0.92s vs 0.91s on main (1% slower)
📖	Linting Wire with this PR took 12.32s vs 12.22s on main (0% slower)
📖	Linting WordPress with this PR took 8.26s vs 7.68s on main (7% slower)

Here's an example of your CHANGELOG entry:

* Added prefer_type_checking rule.  
  [mildm8nnered](https://github.com/mildm8nnered)
  [#issue_number](https://github.com/realm/SwiftLint/issues/issue_number)

note: There are two invisible spaces after the entry's text.

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