Bug#28846 Use of undocumented Prepared Statements crashes server

ALTER VIEW is currently not supported as a prepared statement
and should be disabled as such as they otherwise could cause server crashes.

ALTER VIEW is currently not supported when called from stored
procedures or functions for related reasons and should also be disabled.

This patch disables these DDL statements and adjusts the appropriate test
cases accordingly.

Additional tests has been added to reflect on the fact that we do support
CREATE/ALTER/DROP TABLE for Prepared Statements (PS), Stored Procedures (SP)
and PS within SP.

sql/sql_parse.cc

@@ -4876,6 +4876,10 @@ create_sp_error:
 #endif // ifndef DBUG_OFF
   case SQLCOM_CREATE_VIEW:
     {
+      /*
+        Note: SQLCOM_CREATE_VIEW also handles 'ALTER VIEW' commands
+        as specified through the thd->lex->create_view_mode flag.
+      */
       if (end_active_trans(thd))
         goto error;