* InviteDialog: factor out startDmOrSendInvites
Factor out the logic of calling `startDm` or `inviteUsers` to a helper
function. We're going to need to call this from a second location soon, so this
is useful groundwork.
* Add `UnknownIdentityUsersWarningDialog`
* Add unit tests
* Update playwright tests
* Convert if/else to switch statement
* Convert helper functions to React components
* Factor out "onRemove" callback
* Add clarifying comment
