Reapply "camera2 jni: nativeReadValues() can use camera_metadata_ro_entry...

Reapply "camera2 jni: nativeReadValues() can use camera_metadata_ro_entry instead of camera_metadata_entry"

This reverts commit a5dbb9b15325d240ee1b8c8272ee32c3aeefd61b.

With this updated commit we don't return a NULL array instead of a 0
sized array in case entry.count is 0. Camera clients may be expecting a
non-null zero sized array for these cases as well.

Bug: 371223465

Flag: EXEMPT bugfix

Test: Manual GCA
Change-Id: Id06671aa0f78a96c757e587443f73e93ef46ce74
Signed-off-by: Jayant Chowdhary <jchowdhary@google.com>