Revert "chore: Replace deprecated "componentWillMount" with "componentDidMount" (#7259)" (#7329)

This reverts commit c0b8ce4.

Author: mjackson

packages/react-router-native/experimental/StackRoute.js

@@ -35,7 +35,7 @@ class StackContainer extends Component {
     };
   }
 
-  componentDidMount() {
+  componentWillMount() {
     this.pushToStack("down");
   }
 
@@ -435,7 +435,7 @@ class StackRootContainer extends Component {
 }
 
 class RedirectStack extends Component {
-  componentDidMount() {
+  componentWillMount() {
     delete rootStoredLocations[this.props.path];
   }
 

packages/react-router/modules/__tests__/Route-test.js

@@ -238,7 +238,7 @@ describe("A <Route>", () => {
       const history = createHistory();
       const mount = jest.fn();
       class MatchedRoute extends React.Component {
-        componentDidMount() {
+        componentWillMount() {
           mount();
         }