[Guava] Add escape hatches for jar includes.

[jpobst]

We are currently facing 2 issues related to the way Guava packages have been built.

Referencing Guava and Guava.ListenableFuture

After Guava was shipped, Google copied the ListenableFuture type to a separate package for users who did not want to bring in all of Guava. However, this type is also still in the Guava package. Referencing both of these packages causes both the guava.jar and guava-listenablefuture.jar packages to be added to the final application. This results in an error like:

error : java.lang.RuntimeException: com.android.tools.r8.CompilationFailedException: Compilation failed to complete, 
origin: \.nuget\packages\xamarin.google.guava.listenablefuture\1.0.0.5\buildTransitive\net6.0-android31.0\..\..\jar\guava-
listenablefuture.jar : com/google/common/util/concurrent/ListenableFuture.class

This PR adds an opt-out for the guava-listenablefuture.jar package that users can specify in their .csproj to prevent it from being added to the final application. This should prevent the duplicate class error:

<XamarinGoogleGuavaListenableFutureOptOut>true</XamarinGoogleGuavaListenableFutureOptOut>

This workaround was added in Xamarin.Google.Guava.ListenableFuture 1.0.0.7.

We will be working on an automatic fix for this, but hopefully this should unblock people for now.

Multiple Guava Packages

Because guava.jar has traditionally been added as <EmbeddedReferenceJar>, a copy of it is placed inside each Android bindings library that depends on it. If 2 bindings libraries reference different versions of guava.jar then there are duplicate incompatible versions which can cause as error.

Going forward, we will bind guava.jar as <AndroidJavaLibrary>. This mode does not include a copy of guava.jar in the bindings libraries. Instead, it is added from the transitive NuGet package to the final application so only the highest version of it will get added.

However, this may cause issues in the interim until bindings libraries are updated. To facilitate this, an opt-out mechanism has been added that users can add to the .csproj to prevent the NuGet guava.jar from being added to the application. This may prevent the duplicates until bindings can be updated:

<XamarinGoogleGuavaOptOut>true</XamarinGoogleGuavaOptOut>

This workaround was added in Xamarin.Google.Guava 31.1.0.1.

[jpobst]

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