Try to infer DataContext type from the $parent and #named compiled binding path parts

[maxkatz6]

What is the updated/expected behavior with this PR?

Enables shorter and cleaner syntax without explicit casts. Compiler can infer data context type from the same XAML file.

<Window x:Name="MyWindow" x:DataType="vm:TestDataContext">
    <TextBlock Text="{Binding #MyWindow.DataContext.StringProperty}" />
    <TextBlock Text="{Binding $parent[Window].DataContext.StringProperty}" />

What is the current behavior?

Developers need to cast DataContext to specific view model type, because DataContext is an object.

<Window x:Name="MyWindow" x:DataType="vm:TestDataContext">
    <TextBlock Text="{Binding #MyWindow.((vm:TestDataContext)DataContext).StringProperty}" />
    <TextBlock Text="{Binding $parent[Window].((vm:TestDataContext)DataContext).StringProperty}" />

Checklist

• Added unit tests (if possible)?
• Added XML documentation to any related classes?
• Consider submitting a PR to https://github.com/AvaloniaUI/avalonia-docs with user documentation

Fixed issues

Fixes #10957

[avaloniaui-bot]

You can test this PR using the following package version. 11.3.999-cibuild0052425-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]

[avaloniaui-bot]

You can test this PR using the following package version. 11.3.999-cibuild0052429-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]

[timunie]

We should add a note to the docs once this is merged as older versions needs the cast and users may be confused otherwise.

[MrJul]

A small unexpected change to $parent aside, this looks good!
Awesome work, can't wait to remove those ugly casts :)

[maxkatz6]

@MrJul good find. Fixed.

[avaloniaui-bot]

You can test this PR using the following package version. 11.3.999-cibuild0052545-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]