dict_acquire_mdl_shared(): Invoke the correct variant
dict_table_t::parse_name<true>() also when trylock=true,
that is, we are being called from fts_optimize_sync_table().

Ever since commit 82b7c561 (MDEV-24258)
this code was prone to a hang. If another thread requested an
exclusive dict_sys.latch between the time
dict_acquire_mdl_shared<trylock=true>() acquired a shared dict_sys.latch
and dict_table_t::parse_name<false>() was trying to acquire another
shared dict_sys.latch, InnoDB would get into an infinite livelock
of threads, because the futex-based srw-lock implementation prioritizes
exclusive latch requests.

dict_table_t::parse_name(): Rename the template parameter dict_locked
into dict_frozen.