Stop using JNIEnv.Call*Method()

[jonpryor]

Steps to Reproduce

1. Run a Xamarin.Android within Profiler and look at the allocations.
2. Notice that many JniMethodInfo instances are being allocated -- many thousands, depending on project setup.
3. Cry at all the allocations.

The cause of the allocations is that Android.Runtime.JNIEnv is now largely a "legacy" API, superseded by Java.Interop. In order to avoid JNIEnv binding duplication, most of the JNIEnv methods were updated to delegate to Java.Interop:

public static unsafe IntPtr CallObjectMethod (IntPtr jobject, IntPtr jmethod)
{
	return JniEnvironment.InstanceMethods.CallObjectMethod (new JniObjectReference (jobject), new JniMethodInfo (jmethod, isStatic: false)).Handle;
}

For any code using the legacy API, this can be expensive on the GC.

What we should do:

1. Audit the xamarin-android codebase to ensure we're not using JNIEnv.Call*Method() within our own codebase.
2. Strongly suggest that all Java Library Binding projects set $(AndroidCodegenTarget)=XAJavaInterop1.