Add column for indexed XMP metadata.

Partners have requested that we index XMP metadata so that gallery
apps can quickly determine XMP values (such as photosphere camera
parameters) without having to perform their own expensive indexing
of the underlying files on disk.

This change also redacts any location metadata contained in the
indexed metadata, since we can't safely perform dynamic redaction of
database values.

Bug: 148571206
Test: atest --test-mapping packages/providers/MediaProvider
Change-Id: I9be27cbfca037ccc59d3cc4bd4b004bbba51a5a8