Add vertical-perspective projection. Clarify that globe is an adaptive preset.

[birkskyum]

With the expression syntax well underway, it seems there's a clear need for adding the General Perspective projection (general-perspective) in that way that doesn't break later. It serves as a non-adaptive globe until the expression is in.

We can too clarify that the "globe" is, and will stay as, an adaptive preset that use the general-perspective and mercator projections.

Having the genereral-projection option in GL JS early can help us begin preparing for the introduction of the expressions.

• Add projection expression syntax #888

Launch Checklist

• Confirm your changes do not include backports from Mapbox projects (unless with compliant license) - if you are not sure about this, please ask!
• Briefly describe the changes in this PR.
• Link to related issues.
• Include before/after visuals or gifs if this PR includes visual changes.
• Write tests for all new functionality.
• Document any changes to public APIs.
• Post benchmark scores.
• Add an entry to CHANGELOG.md under the ## main section.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.73%. Comparing base (5788145) to head (8fdaf62).

Additional details and impacted files

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  Files         105      105           
  Lines        4683     4683           
  Branches     1323     1323           
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  Hits         4343     4343           
  Misses        340      340           

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[HarelM]

Let me know which PR to review first and if we can/should push this PR or the other one first.

[birkskyum]

This one is ready to merge, so we can begin making GL JS support the non-mercator high-zoom case (with floating point errors, as noted by Jakub), and simply toggling between mercator and general-perspective.

The projection expression work needs some more time.

[HarelM]

Feel free to push this forward.