Introduce a StartChatFlowCoordinator instead of handing a navigation stack to the Screen Coordinator. (#4674)

* Introduce a basic StartChatFlowCoordinator.

* Move the rest of the start chat flow from the screen coordinator into the flow coordinator.

* Add a UI test for the entire start chat flow.

* Refactor CreateRoom… to CreateRoomScreen…

UnitTests/Sources/StartChatViewModelTests.swift

@@ -56,7 +56,7 @@ class StartChatScreenViewModelTests: XCTestCase {
         try await deferredViewState.fulfill()
         
         let deferredAction = deferFulfillment(viewModel.actions) { action in
-            action == .showRoom(withIdentifier: "id")
+            action == .showRoom(roomID: "id")
         }
         context.send(viewAction: .joinRoomByAddress)
         try await deferredAction.fulfill()