MudDialog: Fix content not stretched in fullscreen mode

[danielchalmers]

Description

Apparently this was a regression which I expect was caused by the addition of a Focus Trap. The dialog content was expecting a flex parent, but the focus trap intercepted that.

This adds classes to the MudFocusTrap and the container for the child content so you can apply styles and debug the layout easier by default.

With those extra classes I applied flex to the intemediary components to make the dialog content grow as intended. Flex is the easier way to do this.

Resolves #5651
Resolves #6994

How Has This Been Tested?

visually

Type 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)
• Documentation (fix or improvement to the website or code docs)

Before

After

I had to hide the Scroll to Top FAB in those images because for some reason they are visible over the dialog.

Checklist

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

[danielchalmers]

@henon Title may want to mention that this is a fix or that it only applies to fullscreen

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.09%. Comparing base (28bc599) to head (74443a9).
Report is 77 commits behind head on dev.

Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #8743      +/-   ##
==========================================
+ Coverage   89.82%   90.09%   +0.26%     
==========================================
  Files         412      419       +7     
  Lines       11878    12182     +304     
  Branches     2364     2397      +33     
==========================================
+ Hits        10670    10975     +305     
+ Misses        681      667      -14     
- Partials      527      540      +13     

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[henon]

Thanks!