feat(web): adds numerous GestureSource unit tests

common/web/gesture-recognizer/src/test/auto/headless/gestures/gestureSequence.spec.ts

@@ -85,5 +85,10 @@ describe("GestureSequence", function() {
   it('first sequence test', () => {
     // simulateSelectorInput should be sufficient for sequence emulation; just capture
     // the first selection once kick-started, then add the "fun" hooks for the rest of the test.
+    // We do have to build a selector and complete the first pass to create a Sequence object, after all.
+    //
+    // For equivalent TouchpointCoordinator auto-tests, the HeadlessInputEngine class should work well.
+    // ... it might even be possible here, since we'll always be starting from the 'head' of the
+    // GestureSequence for these tests.  (Later starts fall within the domain of MatcherSelector.)
   });
 });