Add a stub recovery UI.

This allows recovery to work on devices without screen.
The stub recovery UI does nothing except print to stdout.

Test: write 'recovery\n--wipe_data\n--reason=wipe_data_from_ota\n'
      to misc and boot to recovery on a device without screen.
Bug: 33175036

Change-Id: Icde698aa2e2e29f4b3d0532dfd3c6a939ac2bc63

ui.cpp

@@ -80,12 +80,13 @@ static void* InputThreadLoop(void*) {
     return nullptr;
 }
 
-void RecoveryUI::Init() {
+bool RecoveryUI::Init() {
     ev_init(InputCallback, this);
 
     ev_iterate_available_keys(std::bind(&RecoveryUI::OnKeyDetected, this, std::placeholders::_1));
 
     pthread_create(&input_thread_, nullptr, InputThreadLoop, nullptr);
+    return true;
 }
 
 int RecoveryUI::OnInputEvent(int fd, uint32_t epevents) {