"Refinements" to Native Audio Routing API

Change method names to more generic "AcquireJavaProxy" to support
(potentially) multiple proxy types.
Add "Release" method.
Remove JNIEnv* parameter from Acquire and Release methods.
Add Type ID parameter to support (potential) multiple proxy types.
Enforce "singleton" allocation for proxies.
Disallow proxy acquisition for innapropriate players/recorders.
Refactor to make the code clearer.

Bug: 23899814
Change-Id: Iff354ba46547781e0998a9032de96f445d1474b8