Move focus to the screen when using extra keys

A regression from 2afda54 and friends was that you couldn't use the
extra keys and then directly use the keyboard, you would have to click
in the session first.

This commit restores the correct behavior and also adds a visual queue
to the fact that the screen got the focus by fading the controlbar.

kasmweb/app/ui.js

@@ -1874,20 +1874,20 @@ const UI = {
     },
 
     sendEsc() {
-        UI.rfb.sendKey(KeyTable.XK_Escape, "Escape");
+        UI.sendKey(KeyTable.XK_Escape, "Escape");
     },
 
     sendTab() {
-        UI.rfb.sendKey(KeyTable.XK_Tab, "Tab");
+        UI.sendKey(KeyTable.XK_Tab, "Tab");
     },
 
     toggleCtrl() {
         const btn = document.getElementById('noVNC_toggle_ctrl_button');
         if (btn.classList.contains("noVNC_selected")) {
-            UI.rfb.sendKey(KeyTable.XK_Control_L, "ControlLeft", false);
+            UI.sendKey(KeyTable.XK_Control_L, "ControlLeft", false);
             btn.classList.remove("noVNC_selected");
         } else {
-            UI.rfb.sendKey(KeyTable.XK_Control_L, "ControlLeft", true);
+            UI.sendKey(KeyTable.XK_Control_L, "ControlLeft", true);
             btn.classList.add("noVNC_selected");
         }
     },
@@ -1895,10 +1895,10 @@ const UI = {
     toggleWindows() {
         const btn = document.getElementById('noVNC_toggle_windows_button');
         if (btn.classList.contains("noVNC_selected")) {
-            UI.rfb.sendKey(KeyTable.XK_Super_L, "MetaLeft", false);
+            UI.sendKey(KeyTable.XK_Super_L, "MetaLeft", false);
             btn.classList.remove("noVNC_selected");
         } else {
-            UI.rfb.sendKey(KeyTable.XK_Super_L, "MetaLeft", true);
+            UI.sendKey(KeyTable.XK_Super_L, "MetaLeft", true);
             btn.classList.add("noVNC_selected");
         }
     },
@@ -1906,16 +1906,29 @@ const UI = {
     toggleAlt() {
         const btn = document.getElementById('noVNC_toggle_alt_button');
         if (btn.classList.contains("noVNC_selected")) {
-            UI.rfb.sendKey(KeyTable.XK_Alt_L, "AltLeft", false);
+            UI.sendKey(KeyTable.XK_Alt_L, "AltLeft", false);
             btn.classList.remove("noVNC_selected");
         } else {
-            UI.rfb.sendKey(KeyTable.XK_Alt_L, "AltLeft", true);
+            UI.sendKey(KeyTable.XK_Alt_L, "AltLeft", true);
             btn.classList.add("noVNC_selected");
         }
     },
 
     sendCtrlAltDel() {
         UI.rfb.sendCtrlAltDel();
+        // See below
+        UI.rfb.focus();
+        UI.idleControlbar();
+    },
+
+    sendKey(keysym, code, down) {
+        UI.rfb.sendKey(keysym, code, down);
+        // move focus to the screen in order to be able to
+        // use the keyboard right after these extra keys
+        UI.rfb.focus();
+        // fade out the controlbar to highlight that
+        // the focus has been moved to the screen
+        UI.idleControlbar();
     },
 
 /* ------^-------