Reset mouse release state after restarting the screen

When we temporarily disable the screen (e.g. during TermMessage or
RunInteractiveShell), if the mouse is pressed when the screen is still
active and then released when the screen is already stopped, we aren't
able to catch this mouse release event, so we erroneously think that the
mouse is still pressed after the screen is restarted. This results in
wrong behavior due to a mouse press event treated as a mouse move event,
e.g. upon the left button click we see an unexpected text selection.

So need to reset the mouse release state to "released" after restarting
the screen, assuming it is always released when the screen is restarted.

internal/screen/screen.go

@@ -22,6 +22,10 @@ var Screen tcell.Screen
 // Events is the channel of tcell events
 var Events chan (tcell.Event)
 
+// RestartCallback is called when the screen is restarted after it was
+// temporarily shut down
+var RestartCallback func()
+
 // The lock is necessary since the screen is polled on a separate thread
 var lock sync.Mutex
 
@@ -134,6 +138,10 @@ func TempStart(screenWasNil bool) {
 	if !screenWasNil {
 		Init()
 		Unlock()
+
+		if RestartCallback != nil {
+			RestartCallback()
+		}
 	}
 }