[illink] Try to avoid using SLE in JniRuntime/ManagedPeer

[radekdoulik]

Possible savings, measured by not calling ManagedPeer.Init (), which leads to calling static ctor with registration of methods using SLE and that is pulling a lot of code/API in during linking:

Size difference in bytes ([*1] apk1 only, [*2] apk2 only):
  -          27 assemblies/Mono.Android.dll
  -          30 assemblies/System.Collections.Concurrent.dll
  -         989 assemblies/System.Linq.dll
  -       2,930 assemblies/Java.Interop.dll
  -       4,514 assemblies/System.Collections.dll *1
  -       4,874 assemblies/System.ObjectModel.dll *1
  -       7,987 assemblies/System.Private.CoreLib.dll
  -     115,284 assemblies/System.Linq.Expressions.dll *1
Summary:
  -     136,635 Assemblies -14.87% (of 918,689)
  -     139,506 Package size difference -1.79% (of 7,780,819)

I think we don't use com.xamarin.java_interop.ManagedPeer anywhere (yet?), so we hopefully don't need to register its methods.

I will look into that and either try to remove it or find out whether it would be at least possible to replace SLE usage.

[radekdoulik]

Turned out the Java.Interop tests are using ManagedPeer, so we ended with different solution. We add abstract ActivatePeer method to JniValueManager and have different implementations for desktop MonoRuntimeValueManager and mobile AndroidValueManager. The mobile is using existing code from XA's Java.Interop.TypeManager, which uses System.Reflection.Emit.

The SRE code is a lot more linker friendly than the SLE code and results in substantial size savings.