Use `InputEvent` for text input and set appropriate values for the
`composed`, `data`, `isComposing`, and `inputType` attributes. Use a
placeholder for `dataTransfer` attribute and `getTargetRanges` function,
as they are only applicable to contenteditable, which isn't implemented.
Testing: I added two tests under `tests/wpt/mozilla/tests/input-events`
based on the similarly named ones for contenteditable under
`tests/wpt/tests/input-events`.
Fixes: https://github.com/servo/servo/issues/36398
---------
Signed-off-by: Excitable Snowball <excitablesnowball@gmail.com>
