Code review fixes from 8.0 work: misc

Backport miscellaneous fixes from 8.0 work to lower branches:

• (5.6, 5.7) thd_flush_log_at_trx_commit: replace void* arg with THD* one
• (5.6, 5.7, 8.0) split ut_a / ut_ad DBUG_ASSERT logical conjunctions to separate asserts
• (5.6, 5.7) remove extra space in innodb_sched_priority_master_update warning message
• (5.6, 5.7) mark lock0wait.cc:print_lock_wait_timeout static
• (5.6, 5.7) ut0ut.cc: do not include btr0types.h
• (5.6, 5.7) mysql_unix_socket_connect: use HAVE_PSI_FILE_INTERFACE instead of HAVE_PSI_INTERFACE, replace PSI_server calls with PSI_FILE_CALL macro, restructure the PFS annotation to match the common style
• (5.6, 5.7, 8.0) audit_log plugin: a lot of variables and functions should be marked static, then unused ones removed.
• (5.6, 5.7, 8.0) mark Percona additions in sql_show.cc static
• (5.6, 5.7, 8.0) move extern void init_log_slow_verbosity, init_slow_query_log_use_global_control, init_log_slow_sp_statements declarations from mysqld.cc to set_var.h
• (5.6, 5.7) make row0mysql.cc:column_zip_set_alloc static
• (5.7, 8.0) mark Fill_global_temporary_tables fields const as possible
• (5.7) remove Query_dumpvar::set_var_items
• (5.7) mark Find_thd_with_id::m_daemon_allowed const
• (5.7) fix doxygen typo for dict_get_dictionary_info_by_id
• (5.7) fix doxygen duplication for os_file_advise
• (5.7) innodb_buffer_pool_size_validate warning message "Cannot update innodb_buffer_pool_size to less than 20MB per instance innodb_empty_free_list = backoff." is missing a word
• (5.7, 8.0) remove several unused encryption-related declarations
• (5.7, 8.0) use table_id_t as appropriate in Percona InnoDB patches
• (8.0) use page_no_t and space_id_t as appropriate in Percona InnoDB patches
• (8.0) fix INCLUDE_DIRECTORIES(SYSTEM dir SYSTEM dir ..) in unittest/gunit/keyring_vault/CMakeLists.txt