AVIF omits to select shared constraints from MIAF

[cconcolato]

MIAF defines constraints (Section 8) that can be shared by profiles, but they have to be explicitly selected. Among them is 'self-containment', which is assumed in AVIF but not explicitly stated. The others are: "single-layer", "grid-limit", "single-track", "edit-lists", "matched-duration". AVIF should clarify which ones are applicable.