TAS Input: Enable hotkeys and controller input when Input has focus

Enable emulator hotkeys and controller input (when that option is
enabled) when a TAS Input window has focus, as if it was the render
window instead.  This allows TASers to use frame advance and the like
without having to switch the focused window or disabling Hotkeys Require
Window Focus which also picks up keypresses while other apps are active.

Cursor updates are disabled when the TAS Input window has focus, as
otherwise the Wii IR widget (and anything else controlled by the mouse)
becomes unusable. The cursor continues to work normally when the render
window has focus.

Source/Core/DolphinQt/TAS/TASInputWindow.cpp

@@ -6,7 +6,9 @@
 #include <cmath>
 #include <utility>
 
+#include <QApplication>
 #include <QCheckBox>
+#include <QEvent>
 #include <QGroupBox>
 #include <QHBoxLayout>
 #include <QLabel>
@@ -17,6 +19,7 @@
 
 #include "Common/CommonTypes.h"
 
+#include "DolphinQt/Host.h"
 #include "DolphinQt/QtUtils/AspectRatioWidget.h"
 #include "DolphinQt/QtUtils/QueueOnObject.h"
 #include "DolphinQt/Resources.h"
@@ -268,3 +271,16 @@ std::optional<ControlState> TASInputWindow::GetSpinBox(TASSpinBox* spin, int zer
 
   return (spin->GetValue() - zero) / scale;
 }
+
+void TASInputWindow::changeEvent(QEvent* const event)
+{
+  if (event->type() == QEvent::ActivationChange)
+  {
+    const bool active_window_is_tas_input =
+        qobject_cast<TASInputWindow*>(QApplication::activeWindow()) != nullptr;
+
+    // Switching between TAS Input windows will call SetTASInputFocus(true) twice, but that's fine.
+    Host::GetInstance()->SetTASInputFocus(active_window_is_tas_input);
+  }
+  QDialog::changeEvent(event);
+}