Add automation support via WebDriver

[rakuco]

This PR integrates with the automation concepts defined in https://w3c.github.io/sensors/#automation to allow providing motion or orientation readings via virtual sensors through the WebDriver extension commands defined there.

IMPORTANT: This does not mean that this specification requires implementations to support the Generic Sensor API specification and its derived specifications. Only the Automation section is being referenced, and when necessary some algorithms and definitions are being duplicated here, especially for Device Motion automation.

Device Orientation:

• The "absolute-orientation-euler" and "relative-orientation-euler" virtual sensor types are defined in this specification, along with a parsing algorithm that reads alpha, beta and gamma doubles.

Device Motion:

• Readings are controlled via the "accelerometer", "linear-acceleration" and "gyroscope" virtual sensor types. They are defined in the Accelerometer and Gyroscope specifications. A fallback path for implementations that do not support those specs has been provided.

Fixes #122.

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[rakuco]

@reillyeon PTAL. This depends on w3c/sensors#475.

I'm not a fan of how hand-wavy this spec is in a lot of places, and the bit in https://w3c.github.io/deviceorientation/#deviceorientation that acts on a significant change in orientation is not checking the virtual sensors.

[rakuco]

Thank you for the review, @reillyg!