Windowscommunitytoolkit: [Feature] Update Designer Metadata to new VS2019 Model

[michael-hawker]

Describe the problem this feature would solve

In VS 2019 they changed the model on how the designer loads metadata for components. See article here: https://github.com/microsoft/xaml-designer-extensibility/blob/master/documents/xaml-designer-extensibility-migration.md

The toolkit should update our designer metadata assemblies to align to this new pattern.

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[michael-hawker]

Just realizing the new C# source generator features could help with this in the future, no?

[michael-hawker]

@Nirmal4G has volunteered to take a look at this initial investigation, thank you so much for taking a look, let us know what you find! 🦙❤

Let us know if this looks straight-forward.

(FYI, our code-complete for 6.1 is May 21st; however, I think this would constitute a breaking change, even though it's been long-overdue. So, we'd probably just delegate it to the 7.0 release later this summer when making any required changes can be done without problems.)

[Nirmal4G]

I'm working on it, but I don't know how l was unassigned. Somehow deleting the previous comment removed my assignment.

[michael-hawker]

@Nirmal4G no worries, GitHub is odd sometimes, I've placed it back to you. Thanks for taking a look!

[michael-hawker]

@Nirmal4G was just wondering if you had any luck in figuring this out or not yet? Thanks!

FYI @azchohfi

[Nirmal4G]

Got it working last night. I didn't have the chance to clean it up yet. Tried Roslyn Generators but lack of documentation and a code writer forced me to modify the current source. Still have the implementation though. I'll create a draft PR this weekend for a review.

[michael-hawker]

That's great @Nirmal4G!!! That's going to be a huge help. We'll take a look at the PR once you have it together. I think it'll be a bit late for our upcoming 6.1 release, but we can look at the scope of changes and evaluate the PR, what's left, and timing then.