Use IMtpDatabase to open file in MTP

We want to first try opening the file in MTP using IMtpDatabase
irrespective of whether we are transcoding or not. This way we won't be
affected by the transcoding default option (A or B) and the decision
will solely rely on what we pass from here.

We can now do this because MtpDatabase now has the ability to pass both
supported and unsupported types to MediaProvider.

BUG=158466651
Test: manual

Change-Id: I20bd260cd11278afa66a9e41db3a5d06bd45a3f6