Add common dependencies in new Dependencies props in template for ease of inclusion

[michael-hawker]

I know we've talked about this, but I don't think we have an issue tracking it yet. Came up in discussion here from #131.

We should include some libraries like the XAML Behaviors, Win2D, Toolkit, in the base new Dependencies.WinUI*.props files to show how this works. Either commented out or included but something we put in the initial PR checklist.

Note that currently WinUI 2 itself is automatically included for UWP/Uno. Should we call that out in the comment for the dependencies file or move that to the Dependencies file to be more discoverable?

Dependent/Related to #144 (as I think we'd want to include things like Toolkit namespaces in that as well once we have it?)

@Arlodotexe @mrlacey thoughts?

[Arlodotexe]

If we could place it in the csproj (or anywhere not split between WinUI 2/3) then we could make it a 1-line import for any library, under all configurations:

  <Import Project="$(RepositoryDirectory)common\Dependencies\CommunityToolkit.WinUI.UI.Controls.props" />

Only issue there is the naming, it'd need to resemble the package name but agnostic of WinUI / UWP