Add support for common PHPUnit arguments when watching

[iandunn]

r42760 added the watch:phpunit task, but it only supports the filtering tests by the group. In ticket:42282#comment:18 @soulseekah asked about adding support PHPUnit filters, etc.

That seems very desirable, and there are other PHPUnit arguments that would be useful too, like filtering by test name, and file.

Rather than building all that from scratch, though, we could switch to using ​phpunit-watcher instead. It already has support for all of those, plus an interactive mode where you can switch between them at will, rather than having to restart the task with different args.

I've been using it lately and it seems to work well¹.

@netweb, it looks like you've contributed to it in the past; do you think it'd work well for Core?

[1] Since Core is such a large repo, we'd probably need to wait until ​#116-phpunit-watcher is merged.

[iandunn]

If ​#33-phpunit-watcher is implemented, that might give us the ability to have an interactive command that toggles the WP_TESTS_SKIP_INSTALL variable from #43432, which would be another great devex improvement.

[netweb]

No objections @iandunn, phpunit-watcher is like Jest for PHPUnit, so I'm fully behind that 💯

Also, this may be of interest Ian, ​https://pestphp.com/ it's Jest for PHPUnit, alas the _watcher_ is not up to scratch yet, but it a project I'll be following development of

[iandunn]

Hmm, Running multiple watchers may not be performant.