[system] Fix ContainerProps export

Container.ts only exports a default component.  ContainerProps contains definitions for Container Props and it should be exported.

Signed-off-by: Jack Zhao <bugzpodder@hotmail.com>

packages/mui-system/src/Container/index.d.ts

@@ -1,5 +1,5 @@
 export { default } from './Container';
-export * from './Container';
+export * from './ContainerProps';
 
 export { default as containerClasses } from './containerClasses';
 export * from './containerClasses';