Always trigger componentWillUnmount in StrictMode (#26842)

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## Summary

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Explain the **motivation** for making this change. What existing problem
does the pull request solve?
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In StrictMode, React currently only triggers `componentWillUnmount` if
`componentDidMount` is defined. This would miss detecting issues like
initializing resources in constructor or componentWillMount, for
example:
```
class Component {
  constructor() {
     this._subscriptions = new Subscriptions();
  }
  componentWillUnmount() {
     this._subscriptions.reset();
  }
}
```

The PR makes `componentWillUnmount` always run in StrictMode.

## How did you test this change?

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`yarn test ci`

DiffTrain build for commit 8110222.

compiled-rn/facebook-fbsource/xplat/js/RKJSModules/vendor/react-test-renderer/cjs/ReactTestRenderer-dev.js

@@ -7,7 +7,7 @@
  * @noflow
  * @nolint
  * @preventMunge
- * @generated SignedSource<<e2649a21f4471fab672f885dc7d27434>>
+ * @generated SignedSource<<35eceb39002aa0301bede117a38f12c0>>
  */
 
 'use strict';
@@ -10293,13 +10293,11 @@ function mountClassInstance(workInProgress, ctor, newProps, renderLanes) {
   }
 
   if (typeof instance.componentDidMount === "function") {
-    var fiberFlags = Update | LayoutStatic;
-
-    if ((workInProgress.mode & StrictEffectsMode) !== NoMode) {
-      fiberFlags |= MountLayoutDev;
-    }
+    workInProgress.flags |= Update | LayoutStatic;
+  }
 
-    workInProgress.flags |= fiberFlags;
+  if ((workInProgress.mode & StrictEffectsMode) !== NoMode) {
+    workInProgress.flags |= MountLayoutDev;
   }
 }
 
@@ -10361,13 +10359,11 @@ function resumeMountClassInstance(workInProgress, ctor, newProps, renderLanes) {
     // If an update was already in progress, we should schedule an Update
     // effect even though we're bailing out, so that cWU/cDU are called.
     if (typeof instance.componentDidMount === "function") {
-      var fiberFlags = Update | LayoutStatic;
-
-      if ((workInProgress.mode & StrictEffectsMode) !== NoMode) {
-        fiberFlags |= MountLayoutDev;
-      }
+      workInProgress.flags |= Update | LayoutStatic;
+    }
 
-      workInProgress.flags |= fiberFlags;
+    if ((workInProgress.mode & StrictEffectsMode) !== NoMode) {
+      workInProgress.flags |= MountLayoutDev;
     }
 
     return false;
@@ -10413,25 +10409,21 @@ function resumeMountClassInstance(workInProgress, ctor, newProps, renderLanes) {
     }
 
     if (typeof instance.componentDidMount === "function") {
-      var _fiberFlags = Update | LayoutStatic;
-
-      if ((workInProgress.mode & StrictEffectsMode) !== NoMode) {
-        _fiberFlags |= MountLayoutDev;
-      }
+      workInProgress.flags |= Update | LayoutStatic;
+    }
 
-      workInProgress.flags |= _fiberFlags;
+    if ((workInProgress.mode & StrictEffectsMode) !== NoMode) {
+      workInProgress.flags |= MountLayoutDev;
     }
   } else {
     // If an update was already in progress, we should schedule an Update
     // effect even though we're bailing out, so that cWU/cDU are called.
     if (typeof instance.componentDidMount === "function") {
-      var _fiberFlags2 = Update | LayoutStatic;
-
-      if ((workInProgress.mode & StrictEffectsMode) !== NoMode) {
-        _fiberFlags2 |= MountLayoutDev;
-      }
+      workInProgress.flags |= Update | LayoutStatic;
+    }
 
-      workInProgress.flags |= _fiberFlags2;
+    if ((workInProgress.mode & StrictEffectsMode) !== NoMode) {
+      workInProgress.flags |= MountLayoutDev;
     } // If shouldComponentUpdate returned false, we should still update the
     // memoized state to indicate that this work can be reused.
 
@@ -19783,10 +19775,12 @@ function invokeLayoutEffectMountInDEV(fiber) {
       case ClassComponent: {
         var instance = fiber.stateNode;
 
-        try {
-          instance.componentDidMount();
-        } catch (error) {
-          captureCommitPhaseError(fiber, fiber.return, error);
+        if (typeof instance.componentDidMount === "function") {
+          try {
+            instance.componentDidMount();
+          } catch (error) {
+            captureCommitPhaseError(fiber, fiber.return, error);
+          }
         }
 
         break;
@@ -23928,7 +23922,7 @@ function createFiberRoot(
   return root;
 }
 
-var ReactVersion = "18.3.0-canary-018c58c9c-20230601";
+var ReactVersion = "18.3.0-canary-811022232-20230601";
 
 // Might add PROFILE later.