Fix onHostPause crash in ReactInstanceManager without feature flag (#55986)

Summary:
Pull Request resolved: #55986

This fixes the `java.lang.AssertionError` crash in `ReactInstanceManager.onHostPause()` for third-party React Native apps (primarily Discord at 95.9% of crashes) using the deprecated bridge mode.

## Problem
When VROS triggers Activity lifecycle transitions that cause two Activity instances to exist simultaneously, the reference equality assertion in `onHostPause()` crashes. D95309454 attempted to fix this by gating behind `ReactNativeFeatureFlags.skipActivityIdentityAssertionOnHostPause()`, but that flag has `ossReleaseStage: 'none'`, meaning OSS users can't benefit from the fix.

## Solution
Instead of gating behind a feature flag, always log a warning instead of crashing with an assertion. This is safe because:
- `ReactInstanceManager` is deprecated bridge-mode code
- The flag's `expectedReleaseValue` is `true` (intended to always skip the assertion)
- The bridgeless architecture (`ReactHostImpl.kt`) already has the same behavior
- This avoids the GitHub export issue where the flag defaults to `false` for OSS

## Stats
- 365 crashes in 14 days across 8 third-party apps
- All Quest devices affected (Q2, Q3, Q3S)
- All active branches (v85, v201, v83)

## Changes
- Modified `onHostPause()` to log a warning via `FLog.w()` instead of crashing via `Assertions.assertCondition()` when the paused activity doesn't match the current activity
- Added null safety for the activity parameter in the log message
- No new imports needed (removed dependency on `ReactNativeFeatureFlags`)

Reviewed By: cortinico

Differential Revision: D95570941

fbshipit-source-id: 2fc377c3ace97d328e8b8cc195e3a30069d0c2aa

Author: shubhamksavita

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/ReactInstanceManager.java

@@ -27,6 +27,7 @@
 import static com.facebook.react.uimanager.common.UIManagerType.FABRIC;
 import static com.facebook.systrace.Systrace.TRACE_TAG_REACT;
 
+import android.annotation.SuppressLint;
 import android.app.Activity;
 import android.content.Context;
 import android.content.Intent;
@@ -593,12 +594,14 @@ public void onUserLeaveHint(@Nullable Activity activity) {
 
   /**
    * Call this from {@link Activity#onPause()}. This notifies any listening modules so they can do
-   * any necessary cleanup. The passed Activity is the current Activity being paused. This will
-   * always be the foreground activity that would be returned by {@link
-   * ReactContext#getCurrentActivity()}.
+   * any necessary cleanup. The passed Activity is the current Activity being paused. This is
+   * expected to be the foreground activity that would be returned by {@link
+   * ReactContext#getCurrentActivity()}. If the passed activity does not match the current activity,
+   * a warning will be logged instead of crashing.
    *
    * @param activity the activity being paused
    */
+  @SuppressLint("ReflectionMethodUse")
   @ThreadConfined(UI)
   public void onHostPause(@Nullable Activity activity) {
     if (mRequireActivity) {
@@ -612,15 +615,15 @@ public void onHostPause(@Nullable Activity activity) {
       }
       Assertions.assertCondition(mCurrentActivity != null);
     }
-    if (mCurrentActivity != null) {
-      Assertions.assertCondition(
-          activity == mCurrentActivity,
+    if (mCurrentActivity != null && activity != mCurrentActivity) {
+      FLog.w(
+          TAG,
           "Pausing an activity that is not the current activity, this is incorrect! "
               + "Current activity: "
               + mCurrentActivity.getClass().getSimpleName()
               + " "
               + "Paused activity: "
-              + activity.getClass().getSimpleName());
+              + (activity == null ? "null" : activity.getClass().getSimpleName()));
     }
     onHostPause();
   }