Avoid mounting tree on mode change if it wasn't commited

Summary:
Changelog: [Internal]

Calls to `surfaceHandler.start()` and `setDisplayMode(DisplayMode::Visible)` in quick succession on different threads can cause a race condition between mount and commit operations.

The mountingCoordinator will try to mount an empty revision without any commits causing it to fail with:
```
TransactionTelemetry.cpp:108: function getCommitStartTime: assertion failed (commitStartTime_ != kTelemetryUndefinedTimePoint)
```
which is called from [Binding.cpp](https://www.internalfb.com/intern/diffusion/FBS/browse/master/xplat/js/react-native-github/ReactAndroid/src/main/java/com/facebook/react/fabric/jni/Binding.cpp?lines=791-791&blame=1).

This change avoids this initial commit by verifying we had at least 1 revision commited before mounting it.

Reviewed By: sammy-SC

Differential Revision: D27430174

fbshipit-source-id: d208d55f02cd218a316d6fea62d0106c2bcb4be8

ReactCommon/react/renderer/mounting/ShadowTree.cpp

@@ -248,7 +248,7 @@ ShadowTree::ShadowTree(
           family));
 
   currentRevision_ = ShadowTreeRevision{
-      rootShadowNode, ShadowTreeRevision::Number{0}, TransactionTelemetry{}};
+      rootShadowNode, INITIAL_REVISION, TransactionTelemetry{}};
 
   mountingCoordinator_ =
       std::make_shared<MountingCoordinator const>(currentRevision_);
@@ -275,7 +275,9 @@ void ShadowTree::setCommitMode(CommitMode commitMode) const {
     revision = currentRevision_;
   }
 
-  if (commitMode == CommitMode::Normal) {
+  // initial revision never contains any commits so mounting it here is
+  // incorrect
+  if (commitMode == CommitMode::Normal && revision.number != INITIAL_REVISION) {
     mount(revision);
   }
 }

ReactCommon/react/renderer/mounting/ShadowTree.h

@@ -124,6 +124,8 @@ class ShadowTree final {
   MountingCoordinator::Shared getMountingCoordinator() const;
 
  private:
+  constexpr static ShadowTreeRevision::Number INITIAL_REVISION{0};
+
   void mount(ShadowTreeRevision const &revision) const;
 
   void emitLayoutEvents(