And here's the wild part: instead of cloning WPT tests, import the
relevant WPT tests that this fixes into our own test suite.
This works by adding a small Ladybird-specific callback in
resources/testharnessreport.js (which is what that file is meant for!)
Note that these run as text tests, and so they must signal the runner
when they are done. Tests using the "usual" WPT harness should just
work, but tests that do something more freestyle will need manual
signaling if they are to be imported.
I've also increased the test timeout here from 30 to 60 seconds,
to accommodate the larger WPT-style tests.
Change `EventHandler::handle_keydown()` to no longer assume the cursor
position's node is always a `DOM::Text`. While this assumption holds
for `HTMLInputElement` that has a shadow DOM with a text node, an empty
`contenteditable` might not have any children. With this change,
`handle_keydown()` creates a new text node if the cursor position's
node is not a text node.
