Viewbox implementation

[donandren]

• What does the pull request do?
  Add Viewbox and simplifies LayoutTransform control
• What is the current behavior?
  we don't have Viewbox
• What is the updated/expected behavior with this PR?

Checklist:

• Added unit tests (if possible)?
• Added XML documentation to any related classes

[grokys]

I created a ViewBoxPage for the control catalog and compared it with the same page in WPF. The results don't look quite right.

WPF looks as I'd expect it to:

However, Avalonia doesn't look right:

Not quite sure what's causing the difference. Is this expected?

[donandren]

updated default of ClipToBounds to true (which i missed initially) to behave as wpf.
I think differences in wpf vs. avalonia are not caused by Viewbox itself.
not sure where they are coming from, but

• GridRowDefinitions with Auto height in a StackPanel definatelly is a complex scenario and could be misleading.
• having Path report it's default bounds might not be working as expected, not sure

anyway made tiny modifications to example page and it look like it's working fine:
https://gist.github.com/donandren/3105ed68cdb4f7871abf15045ae671bf

ps: it look to me that somehow wpf Grid is processing rowdefinitions Auto with * logic, when all rows are Auto and making some smart stuff with stackpanel/grid measurements

[grokys]

Yeah, I was wondering if the problem might be with Grid. Might be worth investigating this separately... Also could you add the ViewboxPage to ControlCatalog? Or I can add it if you'd prefer.

[grokys]

LGTM! Just pushed a quick fix to alphabetically order the pages in ControlCatalog, hope that's OK!