Simulate slow statements only for COM_QUERY and COM_STMT_EXECUTE commands,
to exclude mysqld_stmt_prepare() and mysqld_stmt_close() entries from the log,
as they are not relevant for log_slow_debug.test. This simplifies the test.
Tests for MDEV-18892 failed, because of extra 'Prepare' and 'Close stmt'
entries in the output.
Filtering out PS related entries (where it is necessary).