Package clean-up for Extensions, Animations, and Behaviors

[michael-hawker]

Notice we've had a splintering of some packages and some things with very few things in them.

Going to clean-up this issue and merge things back together.

1. Move Effects shadow stuff back into Extensions (originally had more plans here, but for now doesn't make sense to separate out just Shadows, even if they're the main thing not supported by Uno)
2. Make Animations target Uno - we can make the default layer on Uno the XAML layer for the XAML interop helpers
3. Merge Behavior.Animations back into Behaviors - Not much there, and we see most folks that use Behaviors are also using the Animations package already anyway.

Separate PRs:

• Headered Controls HeaderedControls #109
• Merging AdvancedCollectionView and IncrementalLoadingCollection into a Collections package Create Collections Package #120

May effect #113

Started with 1 as draft, working on 2 next

[michael-hawker]

Yay! Clean build for step 1!

Think have Animations package working for Uno (and defaulting to XAML layer); however, we have like no samples for the Animations currently, so hard to test.

Adding multi-target to Behaviors.Animations quick to see if that sample works on WASM, if so, then we have success! And then will do third step of merging the Behaviors package together.

[michael-hawker]

Have all the refactors/code changes done now. Everything should target Uno. Tested building for all three platforms, seems fine.

Haven't been able to see the existing samples load in WASM though still, so not sure what's going on there. I don't see any Uno errors in the output. Some other Behaviors seem to work alright.

Theoretically though, the Animation APIs should work on Uno now...

Should be good to review now though, rebased on main now that Headers merged.

Most changes are just moving and adjusting sample/test namespaces. Couple of Uno polyfills for .NET Standard 2.0. Largest functional change is making default layer for animations to be the Xaml layer over composition on Uno platforms.

[michael-hawker]

Thought it was specific to #136 - however the Behaviors component won't run on UWP here, with a message about the animations assembly... needs investigation:

8> H:\code\CommunityToolkitWindows\components\Behaviors\heads\Uwp\Behaviors.Uwp.csproj : XamlCompiler error WMC1006: Cannot resolve Assembly or Windows Metadata file 'Type universe cannot resolve assembly: CommunityToolkit.WinUI.Animations, Version=8.0.0.0, Culture=neutral, PublicKeyToken=null.'

[michael-hawker]

Arlo tested that the change wasn't introduced by this PR and the UWP head is broken on the Behaviors.Animations in main as well. Filed #137 for tracking, so we can move forward here. Therefore this PR is ready to merge once reviewed.