Remove unused item metadata after copy/paste in Visual Studio

[ThomasGoulet73]

Fixes #5461

Description

Removes unused item metadata that are automatically added to the project after copy/pasting a xaml file in Visual Studio.

Customer Impact

None.

Regression

No.

Testing

Tested locally by modifying my installed SDK to apply the changes in this PR. It fixed the addition of <XamlRuntime>$(DefaultXamlRuntime)</XamlRuntime> on copy/paste.

Risk

This PR will add <Generator>MSBuild:Compile</Generator> and <XamlRuntime>$(DefaultXamlRuntime)</XamlRuntime> to any Page or ApplicationDefinition item even if globbing is disabled or if they are added manually.

[vishalmsft]

@ThomasGoulet73 Thank you for providing the fix.
Partially the risk portion can be mitigated, if ItemDefinitionGroup is also put under the condition
<ItemDefinitionGroup Condition=" '$(_EnableWindowsDesktopGlobbing)' == 'true' ">

The second portion, where it adds those attributes to any ApplicationDefinition \ Page, need to learn more about implication of that.

The SubType gets removed, if adding following attribute to ItemDefinitionGroup. Not sure, why this can be wrong or right.
<SubType>Designer</SubType>

[ThomasGoulet73]

@vishalmsft I added <SubType>Designer</SubType> and _EnableWindowsDesktopGlobbing condition. I did some testing and I think adding <SubType>Designer</SubType> is fine. I looked at other XAML frameworks and I found out that Uno Platform and Avalonia adds it:
https://github.com/unoplatform/uno/blob/master/src/SolutionTemplate/UnoSolutionTemplate/Shared/UnoQuickStart.Shared.projitems#L45
https://github.com/AvaloniaUI/Avalonia/blob/master/packages/Avalonia/AvaloniaBuildTasks.props#L8

[vishalmsft]

@ThomasGoulet73 Thank you references from other platforms. This helps expect no side-effects.

[vishalmsft]

This has been queued for test pass. Tests will be mainly about build of the Sample WPF application.