Add comment about moving markers

We should add this to throwException so we get these markers earlier.
I've had to rewrite tests that test restarting to account for the delayed
restarting heuristic.

Ideally, we should also be able to restart from within throwException if
we're already ready to restart. Right now we wait until the next yield.

packages/react-reconciler/src/ReactFiberCompleteWork.js

@@ -728,6 +728,13 @@ function completeWork(
         // in the concurrent tree already suspended during this render.
         // This is a known bug.
         if ((workInProgress.mode & BatchedMode) !== NoMode) {
+          // TODO: Move this back to throwException because this is too late
+          // if this is a large tree which is common for initial loads. We
+          // don't know if we should restart a render or not until we get
+          // this marker, and this is too late.
+          // If this render already had a ping or lower pri updates,
+          // and this is the first time we know we're going to suspend we
+          // should be able to immediately restart from within throwException.
           const hasInvisibleChildContext =
             current === null &&
             workInProgress.memoizedProps.unstable_avoidThisFallback !== true;