Editorial: Align with Web IDL specification

[autokagami]

This is an automated pull request to align the spec with the latest Web IDL specification.

Currently the autofix might introduce some awkward code formatting, so please feel free to modify the formatting.

Please file an issue on https://github.com/saschanaz/webidl-updater/issues/new if you think this PR is invalid or should be enhanced.

The following is the validation messages from webidl2.js, which may help understanding this PR:

Validation error at line 12 in fullscreen,0:
  Promise<void> requestFullscreen(optional
          ^ `void` is now replaced by `undefined`. Refer to the [relevant GitHub issue](https://github.com/heycam/webidl/issues/60) for more information.

Validation error at line 22 in fullscreen,0:
  Promise<void> exitFullscreen()
          ^ `void` is now replaced by `undefined`. Refer to the [relevant GitHub issue](https://github.com/heycam/webidl/issues/60) for more information.

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