Implement checkbox for selecting/deselecting individual file paths

Created by: courier-new

A user should be able to individually select or deselect file paths from the replace results, to control what we do and don't create a full changeset for. All results should probably be selected by default, unless the user has toggled off the "select all" (this might need to include new results that stream in after toggling has occurred).

In conjunction with https://github.com/sourcegraph/sourcegraph/issues/39195, we should figure out an effective way for tracking which files are selected/deselected. If there are 10000 files and the user deselects 1, it's probably better to say "all files except x" rather than "these 9999 files."