Add text-vs-name cross-type operators, and unify name_ops with text_ops.

Add text-vs-name cross-type operators, and unify name_ops with text_ops.

Now that name comparison has effectively the same behavior as text
comparison, we might as well merge the name_ops opfamily into text_ops,
allowing cross-type comparisons to be processed without forcing a
datatype coercion first.  We need do little more than add cross-type
operators to make the opfamily complete, and fix one or two places
in the planner that assumed text_ops was a single-datatype opfamily.

I chose to unify hash name_ops into hash text_ops as well, since the
types have compatible hashing semantics.  This allows marking the
new cross-type equality operators as oprcanhash.

(Note: this doesn't remove the name_ops opclasses, so there's no
breakage of index definitions.  Those opclasses are just reparented
into the text_ops opfamily.)

Discussion: https://postgr.es/m/15938.1544377821@sss.pgh.pa.us