Fix RCTInstance self-deadlock during invalidate

Summary:
`-[RCTInstance invalidate]` held `_invalidationMutex` while it synchronously called `[_surfacePresenter suspend]`. Stopping surfaces notifies mount observers on the calling thread, and any observer that reaches `callFunctionOnJSModule:` (e.g. `RCTLog` forwarding to JS in debug builds) blocks forever on the same non-recursive mutex.

Release the mutex after setting `_valid = false` and unregistering from the inspector, before `suspend`. Re-entrant calls now see `!_valid` and return.

Changelog:
[iOS][Fixed] - Fix deadlock in `RCTInstance` invalidation when a surface observer calls into JS

Differential Revision: D125706316

Author: zeyap

packages/react-native/ReactCommon/react/runtime/platform/ios/ReactCommon/RCTInstance.mm

@@ -183,11 +183,15 @@ - (void)callFunctionOnJSModule:(NSString *)moduleName method:(NSString *)method
 
 - (void)invalidate
 {
-  std::lock_guard<std::mutex> lock(_invalidationMutex);
-  _valid = false;
-  if (_reactInstance) {
-    _reactInstance->unregisterFromInspector();
+  {
+    std::lock_guard<std::mutex> lock(_invalidationMutex);
+    _valid = false;
+    if (_reactInstance) {
+      _reactInstance->unregisterFromInspector();
+    }
   }
+  // suspend shouldn't be called under _invalidationMutex: it notifies surface observers,
+  // which can call callFunctionOnJSModule and deadlock on the same mutex.
   [_surfacePresenter suspend];
   [_jsThreadManager dispatchToJSThread:^{
     /**