Custom setters implement Equals/GetHashCode and have optimized code gen

[MrJul]

What does the pull request do?

This pull request updates the XamlX IL compiler to kekekeks/XamlX#65 (please see that PR for full details).

It also implements Equals, GetHashCode and IXamlILOptimizedEmitablePropertySetter on custom property setters to take advantage of the XamlX changes and generate fewer IL instructions.

What is the updated/expected behavior with this PR?

Equals and GetHashCode overrides allow the IL compiler to cache the generated dynamic setter methods when possible.
IXamlILOptimizedEmitablePropertySetter generates smaller IL code for static setters.
Everything should work the same as before, but with smaller assemblies emitted from XAML code.

Setters for IBinding and UnsetValueType now use AllowRuntimeNull = false to keep the same behavior as before (that setting wasn't respected before the XamlX PR: the generated code didn't allow null in practice).

Tests

New unit tests have been added to XamlX.
Avalonia already has all the relevant tests needed, which should all pass.

[avaloniaui-team]

You can test this PR using the following package version. 0.10.999-cibuild0022862-beta. (feed url: https://nuget.avaloniaui.net/repository/avalonia-all/index.json) [PRBUILDID]

[MrJul]

Rebased the PR onto master and implemented IXamlILOptimizedEmitablePropertySetter on the new AdderSetter class added by the lazy resources feature.

[avaloniaui-team]

You can test this PR using the following package version. 0.10.999-cibuild0022883-beta. (feed url: https://nuget.avaloniaui.net/repository/avalonia-all/index.json) [PRBUILDID]

[danwalmsley]

@MrJul we are unable to merge this because for some reason your repo settings prevent us from updating your branch to master.

[MrJul]

@danwalmsley Sorry, "allow edit by maintainers" was unchecked, should be all good now!

[avaloniaui-team]

You can test this PR using the following package version. 0.10.999-cibuild0023050-beta. (feed url: https://nuget.avaloniaui.net/repository/avalonia-all/index.json) [PRBUILDID]