Fix arrays comparison in CompareOpclassOptions()

Fix arrays comparison in CompareOpclassOptions()

The current code calls array_eq() and does not provide FmgrInfo.  This commit
provides initialization of FmgrInfo and uses C collation as the safe option
for text comparison because we don't know anything about the semantics of
opclass options.

Backpatch to 13, where opclass options were introduced.

Reported-by: Nicolas Maus
Discussion: https://postgr.es/m/18692-72ea398df3ec6712%40postgresql.org
Backpatch-through: 13