MDEV-22811 DDL fails to drop and re-create FTS index

Problem:
========
- InnoDB clears the fts resource when last FTS index is being dropped
if the table has user defined FTS_DOC_ID. While creating the new fts
index, InnoDB expects to have FTS resources.

Fix:
===
fts_drop_index(): Removed the fts resource clear.

fts_clear_all(): Clear the fts resource when there are no new fts
index to be added.

commit_cache_norebuild(), row_merge_drop_indexes():
Tries to call fts resource after removing associated fts index
from table object

mysql-test/suite/innodb_fts/r/innodb-fts-ddl.result

@@ -227,3 +227,10 @@ id	title	body
 1	MySQL Tutorial	DBMS stands for DataBase ...
 3	Optimizing MySQL	In this tutorial we will show ...
 DROP TABLE articles;
+#
+# MDEV-22811 DDL fails to drop and re-create FTS index
+#
+CREATE TABLE t1 (FTS_DOC_ID BIGINT UNSIGNED PRIMARY KEY,
+f1 VARCHAR(200),FULLTEXT fidx(f1))engine=innodb;
+ALTER TABLE t1 DROP index fidx, ADD FULLTEXT INDEX(f1);
+DROP TABLE t1;