Clarify that updateHostComponent is unnecessary in the new flag

We reuse updateHostComponent for HostSingleton and HostHoistables since it
has a somewhat complex path but that means you have to remember when editing
updateHostComponent that it's not just used for that tag.

Luckily with the new flag, this is actually unnecessary since we just need
to mark it for update if any props have changed and then we diff it later.

Author: sebmarkbage

packages/react-reconciler/src/ReactFiberCompleteWork.js

@@ -1160,17 +1160,23 @@ function completeWork(
             return null;
           } else {
             // This is a Hoistable Instance
-            //
-            // We may have props to update on the Hoistable instance. We use the
-            // updateHostComponent path becuase it produces the update queue
-            // we need for Hoistables.
-            updateHostComponent(
-              current,
-              workInProgress,
-              type,
-              newProps,
-              renderLanes,
-            );
+            // We may have props to update on the Hoistable instance.
+            if (diffInCommitPhase && supportsMutation) {
+              const oldProps = current.memoizedProps;
+              if (oldProps !== newProps) {
+                markUpdate(workInProgress);
+              }
+            } else {
+              // We use the updateHostComponent path becuase it produces
+              // the update queue we need for Hoistables.
+              updateHostComponent(
+                current,
+                workInProgress,
+                type,
+                newProps,
+                renderLanes,
+              );
+            }
 
             // This must come at the very end of the complete phase.
             bubbleProperties(workInProgress);
@@ -1192,13 +1198,20 @@ function completeWork(
         const rootContainerInstance = getRootHostContainer();
         const type = workInProgress.type;
         if (current !== null && workInProgress.stateNode != null) {
-          updateHostComponent(
-            current,
-            workInProgress,
-            type,
-            newProps,
-            renderLanes,
-          );
+          if (diffInCommitPhase && supportsMutation) {
+            const oldProps = current.memoizedProps;
+            if (oldProps !== newProps) {
+              markUpdate(workInProgress);
+            }
+          } else {
+            updateHostComponent(
+              current,
+              workInProgress,
+              type,
+              newProps,
+              renderLanes,
+            );
+          }
 
           if (current.ref !== workInProgress.ref) {
             markRef(workInProgress);