user search should match display_name and user_email too by default

[magnus78]

When searching for users from the dashboard it's not always possible to find users even if you know their display name, which is really frustrating.

Please allow matching on display_name and user_email too.

[magnus78]

proposed fix

[SergeyBiryukov]

#16366, #16620, #18183

[magnus78]

If we worry about speed of large networks i don't see why we wouldn't just add an index for these too?

ALTER TABLE users ADD KEY (user_email);
ALTER TABLE users ADD KEY (display_name);

[SergeyBiryukov]

Follow-up: #27304