[MODERATION] user blocking

- Add the ability to block a user via their profile page.
- This will unstar their repositories and visa versa.
- Blocked users cannot create issues or pull requests on your the doer's repositories (mind that this is not the case for organizations).
- Blocked users cannot comment on the doer's opened issues or pull requests.
- Blocked users cannot add reactions to doer's comments.
- Blocked users cannot cause a notification trough mentioning the doer.

Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/540
(cherry picked from commit 687d852480)
(cherry picked from commit 0c32a4fde5)
(cherry picked from commit 1791130e3c)

models/issues/issue_test.go

@@ -451,6 +451,8 @@ func TestIssue_ResolveMentions(t *testing.T) {
 	testSuccess("user2", "repo1", "user1", []string{"nonexisting"}, []int64{})
 	// Public repo, doer
 	testSuccess("user2", "repo1", "user1", []string{"user1"}, []int64{})
+	// Public repo, blocked user
+	testSuccess("user2", "repo1", "user1", []string{"user4"}, []int64{})
 	// Private repo, team member
 	testSuccess("user17", "big_test_private_4", "user20", []string{"user2"}, []int64{2})
 	// Private repo, not a team member