Add undefined return type to map.cameraForBounds

[keichan34]

Closes #3760 "map.cameraForBounds returns undefined which is not mentioned in type definition"

map.cameraForBounds and related internal methods return undefined (which is actually mentioned in the documentation), but the TypeScript type signature didn't match. This is a simple fix to add the undefined type to the type signature.

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 86.73%. Comparing base (b6e1c0a) to head (6091a62).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4096      +/-   ##
==========================================
+ Coverage   86.56%   86.73%   +0.17%     
==========================================
  Files         241      241              
  Lines       32518    32518              
  Branches     2001     2146     +145     
==========================================
+ Hits        28150    28206      +56     
+ Misses       3404     3386      -18     
+ Partials      964      926      -38     

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[HarelM]

Thanks!!