BlazorWebView API review changes: Shared sources

[MackinnonBuck]

Description of Change

Addresses changes to the BlazorWebView API for shared sources.

It should be noted that there are a few items in the linked issue that this PR does not address:

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IBlazorWebView.cs: Confirm how mandatory it is to have this interface instead of deleting it and declaring the handler in terms of the concrete BlazorWebView type. Remove the interface if it's not really needed in our case.

Addressed in #5984.

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RootComponent.cs: Change Parameters to be IReadOnlyDictionary<string, object?>? as long as this doesn't break setting parameters from XAML.

AFAICT, there isn't a convenient way to create a ParameterView from an IReadOnlyDictionary<string, object?> (the ParameterView.FromDictionary() method only accepts an IDictionary<string, object?>).

So, it doesn't seem we would be able to make this change without either copying to a new dictionary or making changes to ParameterView in dotnet/aspnetcore. The former is undesirable and the latter might not be feasible this late in the release cycle.

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RootComponentsCollection.cs: Since the collection is typed as observable, check we do in fact react if the collection is modified. If not we should make it not observable.

We do react if the collection is modified, so no change is required here.

Issues Fixed

Fixes #5905

[SteveSandersonMS]

Great, thanks @MackinnonBuck!

I'd personally prefer it if we still changed https://github.com/dotnet/maui/pull/5982/files#r848252057 but approving now to ensure this can be merged whenever you are ready.

[Eilon]

Beautiful!