Fix tile cover during globe-to-Mercator transition

[SnailBones]

Closes https://github.com/mapbox/gl-js-team/issues/443

Follow up to https://github.com/mapbox/mapbox-gl-js/pull/11988 and https://github.com/mapbox/mapbox-gl-js/pull/12075.

Solves several issues with https://github.com/mapbox/mapbox-gl-js/pull/11988, most critically an issue in mercatorTileCornersInCameraSpace where camera position in Mercator now multiplied by mercatorScale, now correctly multiplied bynumTiles .

I've verified that this function is working as intended with the AABB visualization introduced in https://github.com/mapbox/mapbox-gl-js/pull/12131

• [X] briefly describe the changes in this PR
• [ ] include before/after visuals or gifs if this PR includes visual changes
• [X] write tests for all new functionality
• [ ] post benchmark scores
• [X] manually test the debug page
• [ ] tagged @mapbox/map-design-team @mapbox/static-apis if this PR includes style spec API or visual changes
• [ ] tagged @mapbox/gl-native if this PR includes shader changes or needs a native port
• [X] apply changelog label ('bug', 'feature', 'docs', etc) or use the label 'skip changelog'
• [X] add an entry inside this element for inclusion in the mapbox-gl-js changelog: <changelog>Fix occasional missing tiles at bottom of screen during globe-Mercator transition</changelog>

[akoylasar]

is there a test that validating the fix?

[SnailBones]

is there a test that validating the fix?

@akoylasar Yes, the test here validates the fix. Previously this test was ignored since tiles were missing at the bottom (see https://github.com/mapbox/mapbox-gl-js/pull/11988).

[avpeery]

I am seeing that tile coverage at bottom of globe is resolved! However, tile coverage missing during mercator-to-globe transition at the north pole still:

[SnailBones]

Many thanks for the thorough testing @avpeery! Since https://github.com/mapbox/mapbox-gl-js/issues/12167) is an issue in pole coloring, not tile coverage, I think we're safe to merge in this PR and should address that separately.