.NET MAUI 9: Feature switch to enable compiled bindings with source

[davidbritch]

In .NET MAUI 9, there's a IsXamlCBindingWithSourceCompilationEnabled feature switch that's disabled by default unless the app is built with NativeAOT, or full trimming.

More info: dotnet/maui#24924 (targets RC2)

[jonathanpeppers]

There are a whole list of switches here:

• https://github.com/dotnet/maui/blob/net9.0/docs/design/FeatureSwitches.md

Most of these take the approach:

• By default they are off, so trying not to break anyone and keep existing behavior.
• If a project uses TrimMode=full (Mono, but link everything) or PublishAot=true (NativeAOT) all these switches are turned on in order to solve many trimming warnings. These may change behavior, which is the point of them.

Overall, I don't know if we need to document all of them in detail. @simonrozsival might want to weigh in, if some are more important than others.

[davidbritch]

@jonathanpeppers Already done via another PR (just isn't live because it's in an include file, for including in the new trimming doc).

[davidbritch]

Dupe of #2559