Fix modifier detection for Backspace / Ctrl-H on Windows (#4582)

Windows sends different key events and modifier combinations to theFullscreenRenderer than a tcell FullscreenRenderer on Linux (-tags tcell).
This led to Ctrl+H being misinterpreted (and therefore unbindable) on some Windows builds.

Basically reverts changes to `src/tui/tcell.go` introduced by `a0cabe0`.

src/terminal.go

@@ -496,6 +496,14 @@ const (
 	reqFatal
 )
 
+func isTerminalEvent(et util.EventType) bool {
+	switch et {
+	case reqClose, reqPrintQuery, reqBecome, reqQuit, reqFatal:
+		return true
+	}
+	return false
+}
+
 type action struct {
 	t actionType
 	a string
@@ -5528,7 +5536,7 @@ func (t *Terminal) Loop() error {
 	req := func(evts ...util.EventType) {
 		for _, event := range evts {
 			events = append(events, event)
-			if event == reqClose || event == reqQuit {
+			if isTerminalEvent(event) {
 				looping = false
 			}
 		}

src/tui/tcell.go

@@ -371,10 +371,12 @@ func (r *FullscreenRenderer) GetChar() Event {
 				}
 			case rune(tcell.KeyCtrlH):
 				switch {
+				case ctrl:
+					return keyfn('h')
 				case alt:
 					return Event{AltBackspace, 0, nil}
-				case ctrl, none, shift:
+				case none, shift:
-					return keyfn('h')
+					return Event{Backspace, 0, nil}
 				}
 			}
 		case tcell.KeyCtrlI: