Avoid collation dependence in indexes of system catalogs.

No index in template0 should have collation-dependent ordering, especially
not indexes on shared catalogs.  For most textual columns we avoid this
issue by using type "name" (which sorts per strcmp()).  However there are a
few indexed columns that we'd prefer to use "text" for, and for that, the
default opclass text_ops is unsafe.  Fortunately, text_pattern_ops is safe
(it sorts per memcmp()), and it has no real functional disadvantage for our
purposes.  So change the indexes on pg_seclabel.provider and
pg_shseclabel.provider to use text_pattern_ops.

In passing, also mark pg_replication_origin.roname as using
text_pattern_ops --- for some reason it was labeled varchar_pattern_ops
which is just wrong, even though it accidentally worked.

Add regression test queries to catch future errors of these kinds.

We still can't do anything about the misdeclared pg_seclabel and
pg_shseclabel indexes in back branches :-(