Use BooleanBoxes for default values in DependencyProperty metadata

[h3xds1nz]

Description

While we have SetValue special-cased for BooleanBoxes and a lot of bool-DPs have properly set their default values with BooleanBoxes.TrueBox or BooleanBoxes.FalseBox, there are quite a few outliers as I've noticed today when digging through the boxed booleans on the heap.

Therefore, this PR does 3 things:

1. Replace boxing of unique values in default values with our pre-defined boxes
2. Adjusts MilCodeGen to generate DPs with the pre-defined boxes as well
3. I've declared MS.Internal.KnownBoxes as a global using, since it is used in most of our classes
   3.1) Since we have 1-3 classes there, that doesn't bring any code bloat
   3.2) That means I've removed the usings in all other files

I didn't do anything in Ribbon because it WindowsBase doesn't have internals visible to the assembly.

Customer Impact

Decreases number of booleans by a big amount, decreased memory usage, improved perf slightly.

Regression

No.

Testing

Local build.

Risk

I did most of the work replacement work with either MilCodeGen or regex, but there were a few manual changes, so it should be fine. Note that using the boxes is not a new thing, this just makes sure all boolean DPs use it.

Microsoft Reviewers: Open in CodeFlow

[codecov]

Codecov Report

Attention: Patch coverage is 16.58986% with 181 lines in your changes missing coverage. Please review.

Project coverage is 11.23853%. Comparing base (3cc9d57) to head (52c25da).

Additional details and impacted files

@@                 Coverage Diff                 @@
##                main      #10711         +/-   ##
===================================================
+ Coverage   11.17950%   11.23853%   +0.05902%     
===================================================
  Files           3314        3314                 
  Lines         665182      665185          +3     
  Branches       74668       74667          -1     
===================================================
+ Hits           74364       74757        +393     
+ Misses        589525      589128        -397     
- Partials        1293        1300          +7     

Flag	Coverage Δ
Debug	11.23853% <16.58986%> (+0.05902%)	⬆️

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