[DO-NOT-MERGE] Compiled PropertyPath for setters

[kekekeks]

Currently intended for use in animations.
@jmacato

For now they are quite simple, but already support syntax like
(Visual.RenderTransform):=ScaleTransform.ScaleX
MyProperty :> MyModelType .Foo.Bar
MyProperty as MyModelType .Foo.Bar
Where :> and as are cast operators, and := is type ensuring operator
Type ensuring is needed for animations to be able to switch a property value type somewhere along the path
E. g. if RenderTransform isn't a ScaleTransform, set RenderTransform to a fresh instance of ScaleTransform
Casts are needed for bindings to ensure that property has a correct type to continue.

IPropertyInfo and ClrPropertyInfo provide reflection-free access to regular CLR properties. This is backed by compile time property accessor generation. ReflectionClrPropertyInfo uses provides same interface via reflection and is not used by compiler.

I've also made AvaloniaProperty to implement IPropertyInfo for convenience purposes

[jkoritzinsky]

What's the purpose of the ChildTraversal element in the property paths? Since it can only legally be followed by a Property element and has no state, it should not be represented in the PropertyPath element list and the . that it represents should be handled exclusively by the parser. That way, there's less possibilities for an invalid PropertyPath and a cleaner API for manipulating them.

[kekekeks]

We can remove the child traversal element. I was thinking that it might be useful for type enforcement operator := to keep track of the traversal point, but it's not really required.

[danwalmsley]

closing due to inactivity.