Support `keyCode` and `charCode` fields in KeyboardEventInit for
Speedometer 3.0
Speedometer 3.0 fails because Servo's KeyboardEvent constructor ignores
keyCode and charCode parameters, hardcoding them to 0. This breaks
frameworks
that check `event.keyCode === 13` for Enter key detection. This is how
[Speedometer 3.0 dispatches key
events](8d67f28d02/resources/benchmark-runner.mjs (L166))
vs [Speedometer 2.0
triggerEnter](491acc2d64/resources/tests.mjs (L60)).
Speedometer 3.0 uses the modern KeyboardEvent constructor but passes
[legacy fields like keyCode and
charCode](https://w3c.github.io/uievents/#legacy-dictionary-KeyboardEventInit)
in the init dictionary for backwards
compatibility with older frameworks(for example: backbone.js)
This change uncomments the legacy KeyboardEventInit fields and updates
the constructor to read them from the init dictionary instead of
hardcoding to 0.
Testing: No new tests added.
Fixes: part of https://github.com/servo/servo/issues/16719
Servo running Speedometer3.0 successfully
<img width="1136" height="880" alt="speedometer 3 0"
src="https://github.com/user-attachments/assets/cf5199a5-d88d-4495-ae96-05fa6332b97e"
/>
---------
Signed-off-by: atbrakhi <atbrakhi@igalia.com>
