[WIP] Implement hit detection for WebGL Mapbox Vector Tiles

[gberaudo]

This PR implements hit detection in the MVT WebGL renderer.
This is achieved by using the same technique has for the vector layer renderer, with some additionnal bits to handle the tiles.

This is an early PR (WIP) to share the current state of the work.

For testing, use http://localhost:8080/webgl-vector-tiles.html
This test has been modified to display the selected feature with a different styling, in a separate layer.

To investigate / fix:

• points does not seem to work;
• white countries polygons does not match anything (maybe OK: do the actually exist as features?);
• why only initial zoom level works?
• figure out the issue with Feature/RenderFeature type mismatch in TileGeometry.js;
• update the test to account for the additionnal low-level calls due to hit detection;

[github-actions]

📦 Preview the website for this branch here: https://deploy-preview-15442--ol-site.netlify.app/.

[gberaudo]

Hit detection framebuffer looks correct, whatever the zoom level:

[jahow]

* [ ]  white countries polygons does not match anything (maybe OK: do the actually exist as features?);

In these tiles the countries are not polygons; the water bodies are.