test: rename test-eventtarget-whatwg-*.js

This renames some test filenames to align with the existing
`parallel/test-whatwg-*.js` for consistency.

According to the comment in each file, they are seemingly manually
ported from the `wpt@dom/events` tests.

Signed-off-by: Daeyeon Jeong daeyeon.dev@gmail.com

PR-URL: #43467
Refs: #43461
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>

Author: daeyeon