Add tests for public API surface of BitmapSizeOptions, cleanup the class

[h3xds1nz]

Description

Adds test for the entire public API surface of BitmapSizeOptions.

Beyond that, the following has been code:

• Updated xml doc to reflect the state of things (there were several incorrect claims that are correct in the official documentation / and also now proven via the unit tests, especially the rotation stuff)
• Uses auto-init properties now to allow for the field to be readonly after creation.
• The namespace has been flattened as in all new PRs. This is a separate commit to allow for easy review.

Customer Impact

Better codegen and test coverage on public surface.

Regression

No.

Testing

Local build, unit tests.

Risk

Low.

Microsoft Reviewers: Open in CodeFlow

[codecov]

Codecov Report

Attention: Patch coverage is 78.62595% with 28 lines in your changes missing coverage. Please review.

Project coverage is 11.49764%. Comparing base (3cc9d57) to head (7aa4fea).
Report is 7 commits behind head on main.

Additional details and impacted files

@@                 Coverage Diff                 @@
##                main      #10713         +/-   ##
===================================================
+ Coverage   11.17950%   11.49764%   +0.31813%     
===================================================
  Files           3314        3315          +1     
  Lines         665182      665206         +24     
  Branches       74668       74668                 
===================================================
+ Hits           74364       76483       +2119     
+ Misses        589525      587331       -2194     
- Partials        1293        1392         +99     

Flag	Coverage Δ
Debug	11.49764% <78.62595%> (+0.31813%)	⬆️

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