[jkeui]

Add LcrViewId and use it to group layers by view

Derive LcrViewId from lcr_view_type and lcr_view_id (256 + lcr_view_id
for VIEW_EXPLICIT, otherwise lcr_view_type), expose it through the
decoder API as derived_view_id, and group avmdec composite outputs by it
so that explicit views with different IDs are no longer merged.

Add a view_id option to the xlayer encoder config. It is required, and
validated to be 0-255, for view_type "explicit".