refactor: Migrate to PointerEvents (#6598)

* refactor: Remove checks for PointerEvent support.

* refactor: Deprecate and remove calls to splitEventByTouches.

* refactor: Deprecate and remove calls to setClientFromTouch().

* refactor: Use PointerEvent in place of Event/MouseEvent/TouchEvent/PseudoEvent.

* refactor: Update references to mouse/touch events in code and documentation to reference pointer events.

* refactor: Merge Gesture and TouchGesture

* chore: clang-format changed files

* refactor: Bind and expect PointerEvents instead of MouseEvents.

* refactor: Rename TouchGesture to Gesture.

* fix: Fix test failures.

* chore: clang-format changed files.

* fix: Fix errant _ from merging

* refactor: Clean up dead code in browser_events.ts.

* chore: Update version in deprecation notices to reflect release schedule

* fix: Fixed a bug that caused the browser context menu to not be suppressed in Chrome.

* fix: Re-export Gesture as TouchGesture for backwards compatibility.

* refactor: Deprecate and remove uses of opt_noPreventDefault.

* chore: Fix error message in gesture.ts.

* chore: Removed obsolete todo.

core/flyout_button.ts

@@ -170,7 +170,8 @@ export class FlyoutButton {
     // AnyDuringMigration because:  Argument of type 'SVGGElement | null' is not
     // assignable to parameter of type 'EventTarget'.
     this.onMouseUpWrapper_ = browserEvents.conditionalBind(
-        this.svgGroup_ as AnyDuringMigration, 'mouseup', this, this.onMouseUp_);
+        this.svgGroup_ as AnyDuringMigration, 'pointerup', this,
+        this.onMouseUp_);
     return this.svgGroup_!;
   }
 
@@ -244,9 +245,9 @@ export class FlyoutButton {
   /**
    * Do something when the button is clicked.
    *
-   * @param e Mouse up event.
+   * @param e Pointer up event.
    */
-  private onMouseUp_(e: Event) {
+  private onMouseUp_(e: PointerEvent) {
     const gesture = this.targetWorkspace.getGesture(e);
     if (gesture) {
       gesture.cancel();