Service method to get all flags for a user

I am working on it.

@viren18febS thanks but I just created a merge request for this: https://git.drupalcode.org/project/flag/-/merge_requests/49

Thanks I just caught up the code, it was failing on some cleaned up namespace use statements. We are using this and it's very helpful, thank you @malcomio. I manually reviewed the code, and the abstraction is nice clean-up for the unflagAllByUser()

Please fix https://git.drupalcode.org/issue/flag-3381654/-/jobs/4104065

ramil g → made their first commit to this issue’s fork.

Looks like the issues were corrected, thanks Ramil g. The remaining are unrelated phpstan for other tests, not appropriate to fix here.

Good work, but needs tests