Fix binding related memory leaks

[MrJul]

What does the pull request do?

This PR fixes some memory leaks related to bindings.

What is the current behavior?

When a compiled binding has an AvaloniaProperty or a method in its path, and its source lives longer than the target, then the target is leaked. The same applies for an attached property through a reflection binding.

What is the updated/expected behavior with this PR?

The bindings don't leak.

How was the solution implemented (if it's not obvious)?

Weak events have been used.

Unit tests have been added.

Of the 4 unit tests added, CompiledBinding_To_InpcProperty_With_Alive_Source_Does_Not_Keep_Target_Alive already passed and was added for comparison purposes. The 3 other tests fail without the changes in this PR.

Fixed issues

• Fixes Binding a property in datatemplate via a named control caused memory leak #15444
• Main fix for DataContext bindings in ControlTemplate leak memory #15443 (all instances are collected but one still remains, which is fix: SelectingItemsControl Selection memory Leak #15446)

[avaloniaui-bot]

You can test this PR using the following package version. 11.2.999-cibuild0047606-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]