Try dotnet/java-interop#1323

[jonpryor]

Context: dotnet/java-interop#1323
Context: #9862 (comment)

Does It Build™?

(The expectation is that it does build -- only unit tests are changed in dotnet/java-interop#1323 -- but that the new
JniRuntimeJniValueManagerContract.cs.CreatePeer_ReplaceableDoesNotReplace() test will fail.)`

[jonpryor]

So I expected JniRuntimeJniValueManagerContract.CreatePeer_ReplaceableDoesNotReplace() to fail, but it failed for the wrong reason:

Expected peer1.JniManagedPeerState to have .Replaceable, but was None.

Further investigation was because we weren't hitting this line:

android/src/Mono.Android/Java.Interop/TypeManager.cs

Line 363 in 542cf52

result.SetJniManagedPeerState (JniManagedPeerStates.Replaceable | JniManagedPeerStates.Activatable);

because Runtime.IsGCUserPeer() returned false, because AnotherJavaInterfaceImpl.java does not implement GCUserPeerable.

Okay, fair.

What I no longer remember -- and thus need to dig around for -- is why we're "protect" setting .Replacable with IsGCUserPeer(). Offhand, this feels like something we could always do?