Handle missing viewState gracefully in SurfaceMountingManager.addViewAt (#56389)

Summary:
Pull Request resolved: #56389

Pull Request resolved: #56376

Changelog:

[ReactAndroid][Fixed] - Prevented a crash in Fabric mounting by handling missing viewState in SurfaceMountingManager.addViewAt() (log + no-op instead of throwing).

## Problem
`SurfaceMountingManager.addViewAt()` throws `RetryableMountingLayerException` when a view tag is not found in the `tagToViewState` map. This exception is **not handled** in the `IntBufferBatchMountItem` execution path — the retry logic in `MountItemDispatcher` only catches this for `DispatchCommandMountItem`. The exception propagates and crashes the app.

**Crash**: `RetryableMountingLayerException: Unable to find viewState for tag X. Surface stopped: false`
**Process**: `com.oculus.firsttimenux:login`
**Impact**: 44,763 occurrences / 14,674 affected users in 30 days

Logview link: [252c85116a7ab5c4ec93ef3c3373cf9d](https://www.internalfb.com/logview/system_vros_crashes/252c85116a7ab5c4ec93ef3c3373cf9d)

## Root Cause
`addViewAt()` uses `getViewState()` which throws on missing tags, while other methods like `removeViewAt()`, `updateProps()`, `updateLayout()`, and `deleteView()` all use `getNullableViewState()` with graceful null handling (soft exception log + early return). This inconsistency means `addViewAt` is the only mount operation that crashes when encountering a timing-related missing view state.

## Fix
Changed `addViewAt()` to use `getNullableViewState()` for both parent and child tag lookups, matching the established pattern used by `removeViewAt`, `updateProps`, `updateLayout`, and `deleteView`. On null, a soft exception is logged with the `SURFACE_MOUNTING_MANAGER_MISSING_VIEWSTATE` category and the operation returns early.

Reviewed By: cortinico

Differential Revision: D99760257

fbshipit-source-id: 3ee9baadfaf1ccb9094effe5bfc2bf9d14bb4ddb

Author: generatedunixname1074695667417611

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/fabric/mounting/SurfaceMountingManager.kt

@@ -282,15 +282,29 @@ internal constructor(
       return
     }
 
-    val parentViewState = getViewState(parentTag)
+    val parentViewState = getNullableViewState(parentTag)
+    if (parentViewState == null) {
+      ReactSoftExceptionLogger.logSoftException(
+          ReactSoftExceptionLogger.Categories.SURFACE_MOUNTING_MANAGER_MISSING_VIEWSTATE,
+          ReactNoCrashSoftException("Unable to find viewState for tag: [$parentTag] for addViewAt"),
+      )
+      return
+    }
     if (parentViewState.view !is ViewGroup) {
       val message =
           "Unable to add a view into a view that is not a ViewGroup. ParentTag: $parentTag - Tag: $tag - Index: $index"
       FLog.e(TAG, message)
       throw IllegalStateException(message)
     }
     val parentView = parentViewState.view as ViewGroup
-    val viewState = getViewState(tag)
+    val viewState = getNullableViewState(tag)
+    if (viewState == null) {
+      ReactSoftExceptionLogger.logSoftException(
+          ReactSoftExceptionLogger.Categories.SURFACE_MOUNTING_MANAGER_MISSING_VIEWSTATE,
+          ReactNoCrashSoftException("Unable to find viewState for tag: [$tag] for addViewAt"),
+      )
+      return
+    }
     val view = viewState.view
     checkNotNull(view) { "Unable to find view for viewState $viewState and tag $tag" }