Don't read fields of a misaligned ExpandedObjectHeader or AnyArrayType.

Don't read fields of a misaligned ExpandedObjectHeader or AnyArrayType.

UBSan complains about this.  Instead, cast to a suitable type requiring
only 4-byte alignment.  DatumGetAnyArrayP() already assumes one can cast
between AnyArrayType and ArrayType, so this doesn't introduce a new
assumption.  Back-patch to 9.5, where AnyArrayType was introduced.

Reviewed by Tom Lane.

Discussion: https://postgr.es/m/20190629210334[email protected]