Make review state filter a multiselect

[Matthew White]

Right now the review state filter on the submissions page is a single-select. However, we want it to be a multiselect. We tried using a native <select multiple>, but that made for a confusing user experience. One possibility that we're considering is a dropdown like what we have for SubmissionFieldDropdown. (Could we genericize that selection dropdown?) As an alternative, maybe there's a nice external component out there that we could use?

This functionality was also requested on the forum: https://forum.getodk.org/t/multiple-filter-odk-central/36905