MDEV-11602 InnoDB leaks foreign key metadata on DDL operations

Essentially revert MDEV-6759, which addressed a double free of memory
by removing the freeing altogether, introducing the memory leaks.
No double free was observed when running the test suite -DWITH_ASAN.

Replace some mem_heap_free(foreign->heap) with dict_foreign_free(foreign)
so that the calls can be located and instrumented more easily when needed.

storage/innobase/dict/dict0dict.cc

@@ -1701,6 +1701,7 @@ struct dict_foreign_remove_partial
 		if (table != NULL) {
 			table->referenced_set.erase(foreign);
 		}
+		dict_foreign_free(foreign);
 	}
 };
 
@@ -3759,7 +3760,6 @@ dict_foreign_add_to_cache(
 	}
 
 	if (for_in_cache) {
-		/* Free the foreign object */
 		dict_foreign_free(foreign);
 	} else {
 		for_in_cache = foreign;
@@ -3789,10 +3789,9 @@ dict_foreign_add_to_cache(
 				"referenced table do not match"
 				" the ones in table.");
 
-                       if (for_in_cache == foreign) {
-                                mem_heap_free(foreign->heap);
-                        }
-
+			if (for_in_cache == foreign) {
+				dict_foreign_free(foreign);
+			}
 
 			DBUG_RETURN(DB_CANNOT_ADD_CONSTRAINT);
 		}
@@ -3846,7 +3845,8 @@ dict_foreign_add_to_cache(
 							elements removed must
 							be one */
 				}
-				mem_heap_free(foreign->heap);
+
+				dict_foreign_free(foreign);
 			}
 
 			DBUG_RETURN(DB_CANNOT_ADD_CONSTRAINT);

storage/innobase/dict/dict0load.cc

@@ -493,7 +493,7 @@ dict_process_sys_foreign_rec(
 	}
 
 	/* This receives a dict_foreign_t* that points to a stack variable.
-	So mem_heap_free(foreign->heap) is not used as elsewhere.
+	So dict_foreign_free(foreign) is not used as elsewhere.
 	Since the heap used here is freed elsewhere, foreign->heap
 	is not assigned. */
 	foreign->id = mem_heap_strdupl(heap, (const char*) field, len);

storage/xtradb/dict/dict0dict.cc

@@ -1643,6 +1643,7 @@ struct dict_foreign_remove_partial
 		if (table != NULL) {
 			table->referenced_set.erase(foreign);
 		}
+		dict_foreign_free(foreign);
 	}
 };
 
@@ -3597,8 +3598,7 @@ dict_foreign_add_to_cache(
 	}
 
 	if (for_in_cache) {
-		/* Free the foreign object */
-		mem_heap_free(foreign->heap);
+		dict_foreign_free(foreign);
 	} else {
 		for_in_cache = foreign;
 	}
@@ -3622,7 +3622,7 @@ dict_foreign_add_to_cache(
 				" the ones in table.");
 
 			if (for_in_cache == foreign) {
-				mem_heap_free(foreign->heap);
+				dict_foreign_free(foreign);
 			}
 
 			return(DB_CANNOT_ADD_CONSTRAINT);
@@ -3678,7 +3678,7 @@ dict_foreign_add_to_cache(
 							be one */
 				}
 
-				mem_heap_free(foreign->heap);
+				dict_foreign_free(foreign);
 			}
 
 			return(DB_CANNOT_ADD_CONSTRAINT);

storage/xtradb/dict/dict0load.cc

@@ -490,7 +490,7 @@ dict_process_sys_foreign_rec(
 	}
 
 	/* This receives a dict_foreign_t* that points to a stack variable.
-	So mem_heap_free(foreign->heap) is not used as elsewhere.
+	So dict_foreign_free(foreign) is not used as elsewhere.
 	Since the heap used here is freed elsewhere, foreign->heap
 	is not assigned. */
 	foreign->id = mem_heap_strdupl(heap, (const char*) field, len);