pgsql: Check for more Unicode functions during upgrade.

Check for more Unicode functions during upgrade.

When checking for expression indexes that may be affected by a Unicode
update during upgrade, check for a few more functions. Specifically,
check for documented regexp functions, as well as the new CASEFOLD()
function.

Also, fully-qualify references to pg_catalog.text and
pg_catalog.regtype.

Discussion: https://postgr.es/m/399b656a3abb0c9283538a040f72199c0601525c.camel@j-davis.com
Backpatch-through: 18

Branch
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REL_18_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/08aa8f035cea9465813667a219f9895fade80dc6

Modified Files
--------------
src/bin/pg_upgrade/check.c | 13 +++++++++----
1 file changed, 9 insertions(+), 4 deletions(-)