DeviceOrientationEvent: Define absolute's value on error

[rakuco]

We were only requiring alpha, beta, and gamma to be null. It makes sense to also require implementations to set absolute to the same value as well.

At the time of writing, this is done for completeness' sake though:

• Blink implements this behavior and sets absolute to false when a deviceorientation cannot be provided, and to true for deviceorientationabsolute events.
• Gecko does not send any events if it cannot provide readings (e.g. when there are no sensors available).
• WebKit only ships an iOS implementation, whose IDL does not even have an absolute attribute.

Fixes #119.

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Preview | Diff

[rakuco]

Accompanying web test in https://github.com/web-platform-tests/wpt/pull/44557

[rakuco]

For posterity:

• Gecko does not send any events if it cannot provide readings (e.g. when there are no sensors available).

• EnableSensorNotifications() is a void function
  • https://searchfox.org/mozilla-central/rev/9bb5d5f55da6cc7163dd93825c25609b769822f9/hal/windows/WindowsSensor.cpp#99
  • https://searchfox.org/mozilla-central/rev/9bb5d5f55da6cc7163dd93825c25609b769822f9/hal/cocoa/CocoaSensor.mm#76
  • https://searchfox.org/mozilla-central/rev/9bb5d5f55da6cc7163dd93825c25609b769822f9/mobile/android/geckoview/src/main/java/org/mozilla/gecko/GeckoAppShell.java#604
• I've also tested the latest Firefox stable release on a Windows laptop without sensors and the deviceorientation event wasn't fired.

• WebKit only ships an iOS implementation, whose IDL does not even have an absolute attribute.

• https://github.com/WebKit/WebKit/blob/469854527dff2f93b810a9be7b0be50b380183b5/Source/WebCore/dom/DeviceOrientationEvent.idl#L38