Scheduling Profiler: Improve warnings and add unit tests (#22038)

* Scheduling Profiler: Updated instructions to mentioned v18+ requirement

* Moved long-event warning to post processing

This lets us rule out non-React work or React work that started before the event and finished quickly during the event.

Also added unit tests for this warning and the various cases.

* Moved long-event warning to post processing

This lets us rule out non-React work or React work that started before the event and finished quickly during the event.

Also added unit tests for this warning and the various cases.

* Updated nested update warning text

* Udpate warning about suspending outside of a transition

Handle edge case where component suspends before the first commit (and label metadata) has been logged.

Add unit tests.

* Fixed logic error in getBatchRange() with minStartTime

* PR feedback: Combined a conditional statement

Author: Brian Vaughn

packages/react-devtools-scheduling-profiler/src/SchedulingProfiler.css

@@ -54,6 +54,7 @@
 .WelcomeInstructionsListItemLink {
   color: var(--color-link);
   margin-left: 0.25rem;
+  margin-right: 0.25rem;
 }
 
 .ImportButtonLabel {

packages/react-devtools-scheduling-profiler/src/SchedulingProfiler.js

@@ -86,7 +86,7 @@ const Welcome = ({onFileSelect}: {|onFileSelect: (file: File) => void|}) => (
         target="_blank">
         profiling build of ReactDOM
       </a>
-      .
+      (version 18 or newer).
     </li>
     <li className={styles.WelcomeInstructionsListItem}>
       Open the "Performance" tab in Chrome and record some performance data.