Bug 1839711 [wpt PR 40679] - [EditContext] Move some tests to WPT, a=testonly

Bug 1839711 [wpt PR 40679] - [EditContext] Move some tests to WPT, a=testonly

Automatic update from web-platform-tests
[EditContext] Move some tests to WPT

Move some existing tests to external/wpt so they can eventually be used
by other implementations.

Tests using eventSender.keyDown() are converted to use
test_driver.send_keys() since only the latter is available in WPT.

Tests using textInputController were not converted, since
textInputController isn't available yet in WPT.

The test case 'Testing attaching EditContext AFTER the element is
focused.' is modified to remove a dependency on the prior test for
making the element initially focusable.

Bug: 999184
Change-Id: I70d21e8ec90ff54f23bf06d021463aedae0d3c37
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4633900
Commit-Queue: Dan Clark <daniec@microsoft.com>
Reviewed-by: Koji Ishii <kojii@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1161270}

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wpt-commits: ad742e32456a77261a254e28217c97e24e532aa6
wpt-pr: 40679