MediaFormat.java: Add KEY_MAX_WIDTH and KEY_MAX_HEIGHT

KEY_MAX_WIDTH and KEY_MAX_HEIGHT are optional video decoder
format keys.  Specify both to request seamless resolution-
change support from video decoders that support this feature.
You can check this via CodecCapabilities.isFeatureSupported.

The codecs use the MAX_WIDTH/HEIGHT values as hints for the
range of resolutions that needs to be supported.  Note,
however, that some codecs may require more memory just by
_preparing_ for larger maximum resolutions, whether or not
that resolution is actually used.

Change-Id: I00fe986ef894fec4bb39bceed081da0e88725d59
Signed-off-by: Lajos Molnar <lajos@google.com>
Related-to-bug: 7093648