extensions: Add vibrationActuator and dual-rumble effect

[nondebug]

Extends the Gamepad API to support common vibration effects.

The following tasks have been completed:

• [ ] Modified Web platform tests (link to pull request)

Implementation commitment:

• [ ] WebKit (https://bugs.webkit.org/show_bug.cgi?id=248989)
• [ ] Chromium (https://bugs.chromium.org/p/chromium/issues/detail?id=)
• [ ] Gecko (https://bugzilla.mozilla.org/show_bug.cgi?id=)

[nondebug]

This is intended to replace https://github.com/w3c/gamepad/pull/68 which can't be easily rebased on the current version of the spec.

[marcoscaceres]

Just to make it easier to review, it might be good to do a tidy of the underlying document and then send these the changes on top.

[marcoscaceres]

Sent https://github.com/w3c/gamepad/pull/164

[cabanier]

@marcoscaceres @nondebug I don't see these changes reflected in the spec. How long does it take before they're published?

[marcoscaceres]

Oh, they are in the extension spec right now, but we plan to move them over 🔜.