Add new systrace sections in MountingCoordinator (#43408)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/43408

Changelog: [internal]

I think mount operations are taking longer than expected because of a debugging block (that we might remove). This adds some systrace sections to distinguish that from the overall time and confirm this only happens in debug builds.

Reviewed By: sammy-SC

Differential Revision: D54746491

fbshipit-source-id: 317b22b6dcd1ae117ed4a013180df8842bf712f0

packages/react-native/ReactCommon/react/renderer/mounting/MountingCoordinator.cpp

@@ -106,6 +106,8 @@ std::optional<MountingTransaction> MountingCoordinator::pullTransaction()
       mountingOverrideDelegate->shouldOverridePullTransaction();
 
   if (shouldOverridePullTransaction) {
+    SystraceSection section2("MountingCoordinator::overridePullTransaction");
+
     auto mutations = ShadowViewMutation::List{};
     auto telemetry = TransactionTelemetry{};
 
@@ -128,6 +130,9 @@ std::optional<MountingTransaction> MountingCoordinator::pullTransaction()
 
 #ifdef RN_SHADOW_TREE_INTROSPECTION
   if (transaction.has_value()) {
+    SystraceSection section2(
+        "MountingCoordinator::verifyMutationsForDebugging");
+
     // We have something to validate.
     auto mutations = transaction->getMutations();