Add ability to search country field on Participants page

Login as admin Create a new course with short name: CS101 Use user upload tool to upload MDL-70565.csv in order to create and enrol 20 students in the course Navigate to Users > Permissions > User policies in site administration Ensure Country is not selected for Show user identity Navigate to the participants page of your new course Confirm Country filter is not available Navigate to Users > Permissions > User policies in site administration Ensure Country is selected for Show user identity Navigate to the participants page of your new course Confirm Country filter is available Select Country filter Choose Spain & Germany from the Type or select... autocomplete Press Apply filters Confirm only those users from Spain & Germany are listed Change Match: Any to Match: None Press Apply filters Confirm only those users not from Spain & Germany are listed Run unit tests: $ vendor/bin/phpunit user/tests/table/participants_search_test.php