Disallow creating binary-coercible casts involving range types.

Disallow creating binary-coercible casts involving range types.

For a long time we have forbidden binary-coercible casts to or from
composite and array types, because such a cast cannot work correctly:
the type OID embedded in the value would need to change, but it won't
in a binary coercion.  That reasoning applies equally to range types,
but we overlooked installing a similar restriction here when we
invented range types.  Do so now.

Given the lack of field complaints, we won't change this in stable
branches, but it seems not too late for v17.

Per discussion of a problem noted by Peter Eisentraut.

Discussion: https://postgr.es/m/076968e1-0852-40a9-bc0b-117cd3f0e43c@eisentraut.org