Reorganize Xamarin.Android.NamingCustomAttributes.

[atsushieno]

context: dotnet/java-interop#58
dependent on: atsushieno/java.interop@5583d26

Copypasting the changes on Java.Interop

We have complicated module interdependency between this and xamarin-android,
so this set of changes is to fix the situation.
So far, here is the changeset summary:
- Xamarin.Android.NamingCustomAttributes.shproj is moved to xamarin-android
- there will be new Java.Interop.NamingCustomAttributes.shproj which is for
use in this repository. It will be shrinked in the later commits to have
only required bits in Java/Interop.

Now Xamarin.Android.sln has two NamingCustomAttributes.shproj: one for
imported and then slightly stripped version of the original shared project
in xamarin-android, and renamed and then significantly stripped version
in Java.Interop.

Build adjustment comes next.

[jonpryor]

dotnet/java-interop#60 has been merged, so please update the Java.Interop commit hash and finish this work. :-)

[atsushieno]

yay, one less dependency!

[jonpryor]

We shouldn't need JCW_ONLY_TYPE_NAMES anymore; that was a Java.Interop-ism, so that these types wouldn't be exported from Java.Interop.Tools.JavaCallableWrappers.dll (and other assemblies?).

Since the new Java.Interop partial types are notpublic (i.e. implicitly "internal" unless overridden in another partial class...), JCW_ONLY_TYPE_NAMES shouldn't be needed anywhere anymore.

[atsushieno]

I removed those JCW_ONLY_TYPE_NAMES from Android./.cs, while leaving them in Android.Runtime and Java.Interop because at this state it seems quite unwise to make extraneous differences between the corresponding sources in Java.Interop.NamingCustomAttributes and those in this new shared project. Those duplicates could be resolved later, not within this change.

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[jonpryor]

Inclusion of this type seems "odd" given that ExportAttribute is also defined Java.Interop/src/Java.Interop.NamingCustomAttributes.

Should this copy be removed? Ditto RegisterAttribute.cs, ExportFieldAttribute.cs, etc.

[atsushieno]

Removing those copies break build. Since it should be rather dealt by those who work on those registration types (which I guess is likely you) and I have no idea about the ideal state of them, I don't plan to deal with them. You can make different changes once they are merged.