SkJpegGainmapEncoder: Update XMP

Update BaseRendition to BaseRenditionIsHDR. Add parsing for boolean
attributes (in XMP, booleans must be "True" or "False", see details
at https://developer.adobe.com/xmp/docs/XMPNamespaces/XMPDataTypes/).

Change Item:Semantic to GainMap.

Add rdf:parseType="Resource" to list items.

Fix an off-by-one bug in computing SkJpegMultiPictureParameters'
offsets.

Bug: skia:14031
Change-Id: I9f03dee9683e1b8238c82087fef4cab29ec64829
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/664536
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Christopher Cameron <ccameron@google.com>
4 files changed