Fix inconsistencies for v12 (pass 2)

Hello Amit,

Can you also review the following fixes?:
2.1. bt_binsrch_insert -> _bt_binsrch_insert (an internal inconsistency)
2.2. EWOULDBOCK -> EWOULDBLOCK (a typo)
2.3. FORGET_RELATION_FSYNC & FORGET_DATABASE_FSYNC ->
SYNC_FORGET_REQUEST (orphaned after 3eb77eba)
2.4. GetNewObjectIdWithIndex -> GetNewOidWithIndex (an internal
inconsistency)
2.5. get_opclass_family_and_input_type ->
get_opclass_opfamily_and_input_type (an internal inconsistency)
2.6. HAVE_BUILTIN_CLZ -> HAVE__BUILTIN_CLZ (missing underscore)
2.7. HAVE_BUILTIN_CTZ -> HAVE__BUILTIN_CTZ (missing underscore)
2.8. MultiInsertInfoNextFreeSlot -> CopyMultiInsertInfoNextFreeSlot (an
internal inconsistency)
2.9. targetIsArray -> targetIsSubscripting (an internal inconsistency)
2.10. tss_htup -> remove (orphaned after 2e3da03e)

I can't see another inconsistencies for v12 for now, but there are some
that appeared before.
If this work can be performed more effectively or should be
postponed/canceled, please let me know.

Best regards,
Alexander