MDEV-33188 Add option --dir to mariadb-dump

New option works just like --tab, w.r.t output (sql file for table definition
and tab-separated for data).

Compared to --tab it allows --databases and --all-databases.
When --dir is used , it creates directory structure in the output directory,
pointed to by --dir. For every database to be dumped, there will be a directory
with database name.

All options that --tab supports, are also supported by --dir, in particular
--parallel

mysql-test/main/mysqldump.result

@@ -6663,7 +6663,7 @@ drop table t1;
 #
 # End of 10.4 tests
 #
-mariadb-dump: --xml can't be used with --tab.
+mariadb-dump: --xml can't be used with --tab or --dir.
 select @@max_connections into @save_max_connections;
 set global max_connections=10;
 mariadb-dump: Got error: 2002: "Received error packet before completion of TLS handshake. The authenticity of the following error cannot be verified: 1040 - Too many connections" when trying to connect
@@ -6673,3 +6673,8 @@ set global max_connections=@save_max_connections;
 #
 # End of 11.4 tests
 #
+# Content of dump directory
+mtr
+mysql
+test
+# Content of 'test' dump subdirectory

mysql-test/main/mysqldump.test

@@ -3044,3 +3044,13 @@ set global max_connections=@save_max_connections;
 --echo #
 --echo # End of 11.4 tests
 --echo #
+#
+# MDEV-33188 Add option --dir to mariadb-dump
+#
+--mkdir $MYSQLTEST_VARDIR/tmp/dump
+--exec $MYSQL_DUMP --dir=$MYSQLTEST_VARDIR/tmp/dump --all-databases --parallel=10
+--echo # Content of dump directory
+--list_files $MYSQLTEST_VARDIR/tmp/dump
+--echo # Content of 'test' dump subdirectory
+--list_files $MYSQLTEST_VARDIR/tmp/dump/test
+