Improved SystemBackdrop sample

[MGGSK]

Made the sample easier to use.

Description

1. Changed the sample description
2. Added inheritance to the sample page
3. Added a title bar to the sample window
4. The sample window now has a icon
5. The theme of the sample window can now be changed.
6. The sample windows now have a list of backdrops that can be applied. If the user clicks opens the "MicaController" sample and clicks "Change Backdrop" the window won't apply Acrylic.
7. Fixed the xaml sample code having c# comments.

Motivation and Context

The old sample has no info about how the materials look like.

How Has This Been Tested?

Manual

Screenshots:

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 change)

[niels9001]

Would it make sense to change this Button into a ComboBox?

We can also do this in a seperate PR!

[niels9001]

See a bunch of UX nits in my comments.

The textblock is redundant if we use a ComboBox right? We can set the selected backdrop there, and increase the spacing between the 2 comboboxes a bit:

[MGGSK]

See a bunch of UX nits in my comments.

The textblock is redundant if we use a ComboBox right? We can set the selected backdrop there, and increase the spacing between the 2 comboboxes a bit:

I changed the spacing from 12 to 20 px.

[niels9001]

Suggested change

	<local:ControlExample HeaderText="DesktopAcrylicController:"
	<local:ControlExample HeaderText="DesktopAcrylicController"

[niels9001]

/azp run

[marcelwgn]

/azp run

[marcelwgn]

The sample code presenter does not display anything for this sample.

[marcelwgn]

While we are at it, should we give the files more descriptive names?

[MGGSK]

The fix should also fix the DesktopAcrylicController sample code not being shown.

<Content Include="ControlPagesSampleCode\SystemBackdrops\SystemBackdropsSampleBackdropTypes_cs.txt" />
<Content Include="ControlPagesSampleCode\SystemBackdrops\SystemBackdropsSampleBackdropTypes_xaml.txt" />
<Content Include="ControlPagesSampleCode\SystemBackdrops\SystemBackdropsSampleMicaController.txt" />
<Content Include="ControlPagesSampleCode\SystemBackdrops\SystemBackdropsSampleDesktopAcrylicController.txt" />
<Content Include="ControlPagesSampleCode\SystemBackdrops\SystemBackdropsEnsureSystemDQC.txt" />