Support background layer type on globe with terrain3d

[birkskyum]

Towards

• [Feat] Support Terrain in Globe projection #4927

This is a PR mainly for the background layer.

The circle render tests, which uses the background, confirm that the circle layer is also working as expected.
The line render tests are just cleaned up a bit - they had some unused "fill" sources.

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!
• 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 90.76%. Comparing base (e4760d0) to head (22b8f66).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4972      +/-   ##
==========================================
+ Coverage   90.67%   90.76%   +0.08%     
==========================================
  Files         266      266              
  Lines       38170    38174       +4     
  Branches     3208     3184      -24     
==========================================
+ Hits        34610    34647      +37     
+ Misses       2611     2578      -33     
  Partials      949      949              

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[birkskyum]

closed in favor of #4977