XamlX upgrade

[sowelipililimute]

Requires space-wizards/space-station-14#44513

This updates our XamlX to a newer version that lets us more easily support features such as templated controls and data binding without having to try and backport verifiable code fixes to our 5-year-old fork of XamlX.

Breaking Changes

The syntax for multiple style classes has changed from:

<Control.StyleClasses>
  <system:String>Hello</system:String>
  <system:String>World</system:String>
</Control.StyleClasses>

to

<Control StyleClasses="Hello World" />

Closes #2023.

[sowelipililimute]

mostly working but xaml jit is broken on MethodAccessExceptions and i cannot figure out for the life of me what's going on there (needs content changes for how i reorganized the button styles)

[mirrorcult]

this will close #2023 (although i wasnt even aware it was possible to do it with that weird syntax)

[Fildrance]

Looking good. CLI build was doing perfectly fine, VS choked a bit due to multiple targets, but was fine after some package restore. Test fail is obviously due to content not being updated with new StyleClass declaration way. We probably merge this one before conent :) not the other way around.