Retain search when switching between filters on /admin/users

Description

Typical scenario - user has trouble logging in or similar. So I go to the admin screen, search for 'fred', and no results. I then click over to 'blocked' - but I have to retype 'fred'.

Proposal

Retain the search field contents when switching filters on the /admin/users screen.

Documentation blurb

I don't think any additional documentation should be needed for this as the behavior would be more intuitive/expected than the current behavior.