ToggleGroup: Rename Outline to Outlined & Internal cleanup

[danielchalmers]

Description

Please let me know if I did this right and if there's any more I should have changed.

How Has This Been Tested?

Types of changes

• 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 not work as expected)

Checklist

• The PR is submitted to the correct branch (dev).
• My code follows the code style of this project.
• I've added relevant tests.

[codecov]

Codecov Report

Attention: Patch coverage is 72.72727% with 3 lines in your changes are missing coverage. Please review.

Project coverage is 89.87%. Comparing base (28bc599) to head (2df10fe).
Report is 13 commits behind head on dev.

Files	Patch %	Lines
...MudBlazor/Components/Toggle/MudToggleItem.razor.cs	40.00%	0 Missing and 3 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #8616      +/-   ##
==========================================
+ Coverage   89.82%   89.87%   +0.04%     
==========================================
  Files         412      414       +2     
  Lines       11878    11911      +33     
  Branches     2364     2364              
==========================================
+ Hits        10670    10705      +35     
+ Misses        681      676       -5     
- Partials      527      530       +3     

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[danielchalmers]

Getting this out of the way before I make actual changes to make reviewing easier

[henon]

Thanks @danielchalmers

Added to v7.0.0 Migration Guide #8447