Support multiple implementations for hook_field_widget_third_party_settings_form

Weird. The tests are not failing where they are supposed to.

The solution to fixing the test should be in core/modules/field_ui/src/Form/EntityFormDisplayEditForm.php protected function thirdPartySettingsForm().

Adding:
$settings_form[$module] = ($settings_form[$module] ?? []) + $hook(

don't forget field_formatter_third_party_settings_form as well

Seems like trying to fail the test on purpose, changing assertNotEmpty for assertEmpty, also passes the test so I'm clueless about what is happening with that test :(

Seems like it was an issue with not declaring the schema for the new third party setting field.
I also squashed the experiments that I did while I didn't have a proper dev enviroment.

In the last two commits I add just the test, failing in the correct place and the the simple fix.

The test only checks widgets, not formatters but since it was the same fix for both I didn't find it very useful to duplicate testing there.

Thanks for the rapid fix, I like it but I can't RTBC it because I suggested the heart of the change so it would be somewhat RTBC'ing my own code. Maybe others don't quite like the succinct version and want core to elaborate on it? I dunno.

Sorry since this is one of two exceptions I think we need a test for both to prevent a regression more than prove the fix works.

Sure. Added tests for the formatters as well

Looks great now thanks!