Remove SegmentVector abstraction

[mourner]

We introduced SegmentVector class to be able to render layers with >2^16 vertices — by maintaining multiple views ("segments") in the vertex array with different offsets. However, according to WebGL best practices, OES_element_index_uint extension that allows 32-bit vertex indexing as opposed to 16-bit one is universally supported and can be relied upon. We could use it to remove the segments abstraction, using the extension to render >2^16 vertices with a single draw draw call, and removing the complexity around splitting and maintaining segments.

[arindam1993]

We also create a new segment every time a new *-sort-key is encountered.

mapbox-gl-js/src/data/segment.js

Line 30 in 17e12c5

if (!segment || segment.vertexLength + numVertices > SegmentVector.MAX_VERTEX_ARRAY_LENGTH || segment.sortKey !== sortKey) {

The segment.sortKey !== sortKey part