Bk/self sizing month header fixes

[bryankeller]

Details

Fixed self-sizing month header issues:

• Fixes an issue that caused views to flicker as they were incorrectly being reused only for sizing purposes
• Prevent the month header size cache from growing unbounded

I'll leave comments in code where the relevant changes are.

Updated tests:

• Added self-sizing month header tests
• Sorted the comparison strings used in the unit tests to make future diffs smaller

Related Issue

N/A

Motivation and Context

Realized I introduce

How Has This Been Tested

Types of changes

• Docs change / refactoring / dependency upgrade
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.

[bryankeller]

It's easy enough to just maintain a separate dictionary of sizing views. Then there's no chance we'll accidentally use a real month header view from the reuse manager to do sizing.