Camera NDK: New lifecycle for ACameraMetadata_fromCameraMetadata

Instead of requiring the user to call NewGlobalRef/DeleteGlobalRef
for keeping the java object alive when creating an NDK view into it,
reference count the real native data instead, so that there's no need
to keep track of the Java object lifecycle.

- Switch CameraMetadataNative use std::shared_ptr

Test: New CTS tests pass, fail without this CL
Bug: 148972471
Change-Id: I9a00fc1daa1beac35a15484960048facb90499a6