fix: fresh vendor dependencies

[tlgimenes]

What's the purpose of this PR?

This PR solves issues related to running deno vendor on a fresh project.

How does it work?

Vendoring in fresh is a little bit more difficult than in a "normal" deno project because it uses esbuild and, sometimes, dependency resolution is not accessible to deno's engine. To overcome this issue, I'm using a technique of explicitly configuring deno's engine to vendor dependencies by using the dynamic import tag. The upside of this approach is not actually importing the dependency but only configuring the vendoring engine to include this dependency.

This PR fixes both fresh's and twind's plugin missing modules.

How to test it?

To test it, clone this version, link to a newly created fresh project and run:

deno vendor main.ts dev.ts
deno run -A --no-remote main.ts

The server should be spawned without any issues.

[deer]

@marvinhagemeister, this is already working for me with fresh 1.5.4 and deno 1.38.3.

• deno run -Ar https://fresh.deno.dev
• cd vendor_test
• deno vendor main.ts dev.ts
• (delete imports from deno.json because "importMap": "./vendor/import_map.json" was added)
• deno run -A --no-remote dev.ts

Then I get:

The manifest has been generated for 5 routes and 1 islands.

 🍋 Fresh ready
    Local: http://localhost:8000/