[import-w3c-tests] Make --clean-dest-dir work with partial imports

[gsnedders]

3482356

[import-w3c-tests] Make --clean-dest-dir work with partial imports
https://bugs.webkit.org/show_bug.cgi?id=256751

Reviewed by Jonathan Bedard.

We need to do this slightly more lazily, and not just blanket clean
the entire destination directory.

Fix updating resource-files.json to write the file even if we aren't
importing new support files, as might be true of a partial import.

And finally fix removing items from tests-options.json to match
against the correct path, and avoid mutating the object we're
iterating over (which raises an RuntimeError).

* Tools/Scripts/webkitpy/w3c/test_importer.py:
(TestImporter.__init__):
(TestImporter.do_import):
(TestImporter.import_tests):
(TestImporter.remove_slow_from_w3c_tests_options):
* Tools/Scripts/webkitpy/w3c/test_importer_unittest.py:

Canonical link: https://commits.webkit.org/264384@main

dd3da92

Misc	iOS, tvOS & watchOS	macOS	Linux	Windows
✅ 🧪 style	✅ 🛠 ios	✅ 🛠 mac	✅ 🛠 wpe	✅ 🛠 wincairo
✅ 🧪 bindings	✅ 🛠 ios-sim	✅ 🛠 mac-AS-debug	✅ 🧪 wpe-wk2
✅ 🧪 webkitperl	✅ 🧪 ios-wk2	✅ 🧪 api-mac	✅ 🛠 gtk
✅ 🧪 webkitpy	✅ 🧪 ios-wk2-wpt	✅ 🧪 mac-wk1	✅ 🧪 gtk-wk2
	✅ 🧪 api-ios	✅ 🧪 mac-wk2	✅ 🧪 api-gtk
	✅ 🛠 tv	✅ 🧪 mac-AS-debug-wk2
	✅ 🛠 tv-sim
	✅ 🛠 watch
✅ 🛠 🧪 unsafe-merge	✅ 🛠 watch-sim

[webkit-early-warning-system]

EWS run on previous version of this PR (hash e2a657e)

Misc	iOS, tvOS & watchOS	macOS	Linux	Windows
✅ 🧪 style	✅ 🛠 ios	✅ 🛠 mac	✅ 🛠 wpe	✅ 🛠 wincairo
✅ 🧪 bindings	✅ 🛠 ios-sim	✅ 🛠 mac-AS-debug	✅ 🧪 wpe-wk2
✅ 🧪 webkitperl	✅ 🧪 ios-wk2	✅ 🧪 api-mac	✅ 🛠 gtk
✅ 🧪 webkitpy	✅ 🧪 ios-wk2-wpt	✅ 🧪 mac-wk1	✅ 🧪 gtk-wk2
	✅ 🧪 api-ios	✅ 🧪 mac-wk2	✅ 🧪 api-gtk
	✅ 🛠 tv	✅ 🧪 mac-AS-debug-wk2
	✅ 🛠 tv-sim
	✅ 🛠 watch
	✅ 🛠 watch-sim

[gsnedders]

@youennf you'd asked for a unit-test for an earlier version of this in https://bugs.webkit.org/show_bug.cgi?id=235038; this finally does that, and fixes several bugs in the existing code now there's test coverage

[webkit-early-warning-system]

EWS run on current version of this PR (hash dd3da92)

Misc	iOS, tvOS & watchOS	macOS	Linux	Windows
✅ 🧪 style	✅ 🛠 ios	✅ 🛠 mac	✅ 🛠 wpe	✅ 🛠 wincairo
✅ 🧪 bindings	✅ 🛠 ios-sim	✅ 🛠 mac-AS-debug	✅ 🧪 wpe-wk2
✅ 🧪 webkitperl	✅ 🧪 ios-wk2	✅ 🧪 api-mac	✅ 🛠 gtk
✅ 🧪 webkitpy	✅ 🧪 ios-wk2-wpt	✅ 🧪 mac-wk1	✅ 🧪 gtk-wk2
	✅ 🧪 api-ios	✅ 🧪 mac-wk2	✅ 🧪 api-gtk
	✅ 🛠 tv	✅ 🧪 mac-AS-debug-wk2
	✅ 🛠 tv-sim
	✅ 🛠 watch
✅ 🛠 🧪 unsafe-merge	✅ 🛠 watch-sim

[webkit-commit-queue]

Committed 264384@main (3482356): https://commits.webkit.org/264384@main

Reviewed commits have been landed. Closing PR #13929 and removing active labels.