Adaptive bounds calculation

[stepankuzmin]

This PR implements the adaptive bounds calculation proposed here #12199

Alternatively, we could do adaptive bounds calculation similar to the one happening in tile_transform.js for alternative projections — start with 4 corners, and delve recursively into midpoints while they stray too much from Euclidean midpoints. This might still produce a noticeable error, but will at least be a significant improvement to the current results. We should also be careful of the case where midpoint is in the middle but the line gets curvy on either side of the midpoint.

To calculate the globe bounds, it recursively iterates other midpoints of the canvas and raycasts the screen coordinates to the globe, expanding the bounds. It also expands the bounds if poles are visible.

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Launch Checklist

• briefly describe the changes in this PR
• include before/after visuals or gifs if this PR includes visual changes
• write tests for all new functionality
• document any changes to public APIs
• manually test the debug page
• apply changelog label ('bug', 'feature', 'docs', etc) or use the label 'skip changelog'
• add an entry inside this element for inclusion in the mapbox-gl-js changelog: <changelog>Improve the globe bounds calculation</changelog>

[SnailBones]

LGTM, nice work @stepankuzmin! Added one nit about testing coverage.

[mourner]

Nice work!