MDEV-21563 FTS thread aborts during shutdown

- Added the test case in innodb_fts suite
- Updated copyright year in row0mysql.cc

mysql-test/suite/innodb_fts/t/misc_debug2.test

@@ -0,0 +1,11 @@
+--source include/have_innodb.inc
+--source include/have_debug.inc
+--source include/not_embedded.inc
+call mtr.add_suppression("InnoDB: Table '.*' tablespace is set as discarded.");
+
+CREATE TABLE mdev21563(f1 VARCHAR(100), FULLTEXT idx(f1))ENGINE=InnoDB;
+set debug_dbug="+d,fts_instrument_sync_request";
+INSERT INTO mdev21563 VALUES('This is a test');
+ALTER TABLE mdev21563 DISCARD TABLESPACE;
+--source include/restart_mysqld.inc
+DROP TABLE mdev21563;