Remove Blazor Desktop workarounds for iOS/Android Content warnings

The MAUI Blazor Desktop targets contain various workarounds to avoid various warnings related to MSBuild Content items. The workaround to avoid those warning is to use BeforeTargets/AfterTargets to temporarily remove certain Content items, and then later restore them.

Ideally we would have a proper way of avoiding these warnings. Maybe one of these:

1. Do something to avoid getting into this problem in the first place? This might not be possible due to each SDK having its own, incompatible view of what Content means.
2. Have a generic MAUI way of doing the workaround so it isn’t unique to Blazor. Perhaps if Blazor Desktop could tag the items as being MauiWebContent or similar, the MAUI targets could “do the needful” (which might be identical to the current workarounds, but in a common location) (credit: @mattleibow )

[javiercn]

@Eilon Yes, @pranavkm and myself synced offline on what to do here, and we believe we can do this in a way that avoids us having to update this in the future for new Razor features.

We’ll piggyback on Convert…ToMauiAssets and update the content items there based on the list of static web assets as well as the Razor files.

[Eilon]

@javiercn I think @pranavkm has discussed with the Android and iOS SDK folks and we have solutions in progress.