WL#4907: plugin service: functions from plugin.h

Affects: Server-9.x   —   Status: Un-Assigned   —   Priority: Medium

All functions that are listed now in plugin.h should be converted to services,
to enable fine-grained versioning protection.

Possible grouping of functions into services:

THD misc
  thd_get_thread_id
  thd_killed
  set_thd_proc_info
  thd_security_context

THD memory allocations
  thd_make_lex_string
  thd_memdup
  thd_strmake
  thd_strdup
  thd_calloc
  thd_alloc

THD storage engine common:
  thd_set_ha_data
  thd_get_ha_data
  thd_ha_data

THD storage engine advanced
  thd_tablespace_op
  thd_in_lock_tables
  thd_inc_row_count

THD storage engine transactions
  thd_sql_command
  thd_tx_isolation
  thd_test_options
  thd_get_xid

Query cache
  mysql_query_cache_invalidate4

user vars
  get_user_var_str
  get_user_var_real
  get_user_var_int

temp file
  mysql_tmpfile