camera2: Fix backward compatibility breakage for setting metering regions.

With the new entries in sSetCommandMap, the private functions for
setting metering regions cast the input value to MeteringRegion[], which
can break some existing clients which pass in Object[] to
CameraMetadata.set(). We revert to the old behavior of letting Marshaler
handle conversion from Object[] -> MeteringRectangle[] internally.

Bug: 195095702

Test: GCA with different zoom (basic validity)
Test: ITS scene1_1
Test: Camera CTS

Change-Id: Iea372adf76d1c6f81f1c63ff2bd3553ab39f30e4
Signed-off-by: Jayant Chowdhary <jchowdhary@google.com>