Add multitouch support to Gamepad API

Changes and updates have been made to Fernando Attia's patchset 1612050.
The implementation has been changed to support the most recent changes
to the spec w3c/gamepad#168.

Support for DualShock4 controller is part of patch.
This commit is a squash of several changes the last major one is:
Normalize touchIds per Gamepad

The same hardware may provide input to Gamepads in different tabs.
This commit normalizes touchIds coming from the hardware to a single
incremented value starting at zero per Gamepad instance.

Extend the Gamepad API to support multitouch surfaces (touchpads).
Intent to prototype :
https://groups.google.com/a/chromium.org/g/blink-dev/c/4q_k23rPMos

Chrome status entry:
https://www.chromestatus.com/feature/4782975812108288

R=mattreynolds@chromium.org

Change-Id: I0fa2006c3fc36a908b316cc29b97d295aac798ca

Update idl to match current spec draft

Normalize touchid to 32bit value.

Update web tests.

Bug: 1143942
Change-Id: I80ed31ebf0c6a347906b91b3c178099d1e332c53

resources/chromium/webxr-test.js

@@ -1966,6 +1966,7 @@ class MockXRInputSource {
       timestamp: 0n,
       axes: [],
       buttons: [],
+      touchEvents: [],
       mapping: GamepadMapping.GamepadMappingStandard,
       displayId: 0,
     };