Toggle the first-person camera with a right thumbstick click

Clicking the right thumbstick flips first person exactly as the F10
checkbox does, and saves it the same way. It works on the VR controllers
in either presentation (with a short tick on the right controller) and on
any other gamepad while VR is running. It never reached the game: SDL's
stick click only lands in Aurora's extended buttons.

A click counts on release, and only if the left thumbstick stayed up and
the headset settings panel stayed closed throughout, so the two-thumbstick
panel chord in gamepad mode never toggles the camera. A gamepad whose
right stick click is bound to a GameCube control on its port, as a button
or in an input expression, keeps it for the game. The XR side only posts
a request; the toggle itself runs on the game thread with the checkbox.

[vr] first_person_toggle_click (default true) and a checkbox under the
camera toggle turn the click off. mkw_vr_camera_toggle_tests covers the
click rule.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

runtime/tests/vr_camera_toggle_tests.cpp

@@ -0,0 +1,61 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+//
+// The right-thumbstick click that toggles the first-person camera
+// (vr/camera_toggle.h).
+
+#include "vr/camera_toggle.h"
+
+#include <iostream>
+
+namespace {
+
+using mkw::vr::ClickToggle;
+
+int g_failures = 0;
+
+void Check(bool condition, const char* what) {
+    if (!condition) {
+        ++g_failures;
+        std::cerr << "FAILED: " << what << '\n';
+    }
+}
+
+} // namespace
+
+int main() {
+    ClickToggle click;
+    Check(!click.Update(true, false, false), "nothing on press");
+    Check(!click.Update(true, false, false), "nothing while held");
+    Check(click.Update(false, false, false), "a clean click fires on release");
+    Check(!click.Update(false, false, false), "fires once");
+
+    // Both thumbsticks (the gamepad settings-panel chord), in either order.
+    click.Update(true, false, false);
+    click.Update(true, true, false);
+    Check(!click.Update(false, true, false), "right then left: the chord, no toggle");
+    click.Update(false, true, false);
+    click.Update(true, true, false);
+    Check(!click.Update(false, false, false), "left then right: the chord, no toggle");
+
+    // The panel owned the controllers during the press.
+    click.Update(true, false, false);
+    click.Update(true, false, true);
+    Check(!click.Update(false, false, false), "blocked midway: no toggle");
+    click.Update(true, false, false);
+    Check(!click.Update(false, false, true), "blocked at release: no toggle");
+
+    // Recovers for the next clean click.
+    click.Update(true, false, false);
+    Check(click.Update(false, false, false), "a later clean click fires again");
+
+    click.Update(true, false, false);
+    click.Reset();
+    Check(!click.Update(false, false, false), "reset forgets a held press");
+
+    if (g_failures != 0) {
+        std::cerr << g_failures << " check(s) failed\n";
+        return 1;
+    }
+    std::cout << "vr camera toggle tests passed\n";
+    return 0;
+}