MDEV-15945 --ps-protocol does not test some queries

Make mysqltest to use --ps-protocol more

use prepared statements for everything that server supports
with the exception of CALL (for now).

Fix discovered test failures and bugs.

tests:
* PROCESSLIST shows Execute state, not Query
* SHOW STATUS increments status variables more than in text protocol
* multi-statements should be avoided (see tests with a wrong delimiter)
* performance_schema events have different names in --ps-protocol
* --enable_prepare_warnings

mysqltest.cc:
* make sure run_query_stmt() doesn't crash if there's
  no active connection (in wait_until_connected_again.inc)
* prepare all statements that server supports

protocol.h
* Protocol_discard::send_result_set_metadata() should not send
  anything to the client.

sql_acl.cc:
* extract the functionality of getting the user for SHOW GRANTS
  from check_show_access(), so that mysql_test_show_grants() could
  generate the correct column names in the prepare step

sql_class.cc:
* result->prepare() can fail, don't ignore its return value
* use correct number of decimals for EXPLAIN columns

sql_parse.cc:
* discard profiling for SHOW PROFILE. In text protocol it's done in
  prepare_schema_table(), but in --ps it is called on prepare only,
  so nothing was discarding profiling during execute.
* move the permission checking code for SHOW CREATE VIEW to
  mysqld_show_create_get_fields(), so that it would be called during
  prepare step too.
* only set sel_result when it was created here and needs to be
  destroyed in the same block. Avoid destroying lex->result.
* use the correct number of tables in check_show_access(). Saying
  "as many as possible" doesn't work when first_not_own_table isn't
  set yet.

sql_prepare.cc:
* use correct user name for SHOW GRANTS columns
* don't ignore verbose flag for SHOW SLAVE STATUS
* support preparing REVOKE ALL and ROLLBACK TO SAVEPOINT
* don't ignore errors from thd->prepare_explain_fields()
* use select_send result for sending ANALYZE and EXPLAIN, but don't
  overwrite lex->result, because it might be needed to issue execute-time
  errors (select_dumpvar - too many rows)

sql_show.cc:
* check grants for SHOW CREATE VIEW here, not in mysql_execute_command

sql_view.cc:
* use the correct function to check privileges. Old code was doing
  check_access() for thd->security_ctx, which is invoker's sctx,
  not definer's sctx. Hide various view related errors from the invoker.

sql_yacc.yy:
* initialize lex->select_lex for LOAD, otherwise it'll contain garbage
  data that happen to fail tests with views in --ps (but not otherwise).

mysql-test/suite/sys_vars/t/sql_buffer_result_func.test

@@ -46,17 +46,23 @@ INSERT INTO t1 VALUES('aa','bb');
 
 SET SESSION sql_buffer_result = 1;
 
+--disable_ps_protocol
 SHOW STATUS LIKE 'Created_tmp_tables';
+--enable_ps_protocol
 --echo Expected value : 0.
 
 SELECT * FROM t1;
 
+--disable_ps_protocol
 SHOW STATUS LIKE 'Created_tmp_tables';
+--enable_ps_protocol
 --echo Expected value : 1.
 
 SELECT * FROM t1;
 
+--disable_ps_protocol
 SHOW STATUS LIKE 'Created_tmp_tables';
+--enable_ps_protocol
 --echo Expected value : 2.
 
 --echo '#--------------------FN_DYNVARS_156_02-------------------------#'
@@ -66,12 +72,16 @@ SHOW STATUS LIKE 'Created_tmp_tables';
 
 SET SESSION sql_buffer_result = 0;
 
+--disable_ps_protocol
 SHOW STATUS LIKE 'Created_tmp_tables';
+--enable_ps_protocol
 --echo Expected value : 2.
 
 SELECT * FROM t1;
 
+--disable_ps_protocol
 SHOW STATUS LIKE 'Created_tmp_tables';
+--enable_ps_protocol
 --echo Expected value : 2.
 
 --echo '#--------------------FN_DYNVARS_156_03-------------------------#'