[hle,display,overlay,starter,hid] add overlay functions, starter applet (initially), HID handheld for system applets and fw21 stubs (#3080)

Adds fully functional overlay display.
- Enable Overlay Applet via "View" -> "Enable Overlay Display Applet"
- Open the overlay by pressing the home button for over 1s
- Can adjust volume
- Can toggle airplane mode (if on WiFi, maybe if overlay is enabled pretend to be on WiFi?)
- Future TODO(?): Adjust Brightness implementation for host system
- Inputs are properly registered. e.g. if overlay open, application does not register inputs.

You can control volume and airplane mode outside of the emulator window

Reviewed-on: https://git.eden-emu.dev/eden-emu/eden/pulls/3080
Reviewed-by: CamilleLaVey <camillelavey99@gmail.com>
Reviewed-by: crueter <crueter@eden-emu.dev>
Co-authored-by: Maufeat <sahyno1996@gmail.com>
Co-committed-by: Maufeat <sahyno1996@gmail.com>

src/core/hle/service/vi/container.cpp

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: Copyright 2025 Eden Emulator Project
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 // SPDX-FileCopyrightText: Copyright 2024 yuzu Emulator Project
 // SPDX-License-Identifier: GPL-2.0-or-later
 
@@ -131,6 +134,38 @@ Result Container::SetLayerBlending(u64 layer_id, bool enabled) {
     R_SUCCEED();
 }
 
+Result Container::SetLayerZIndex(u64 layer_id, s32 z_index) {
+    std::scoped_lock lk{m_lock};
+
+    auto* const layer = m_layers.GetLayerById(layer_id);
+    R_UNLESS(layer != nullptr, VI::ResultNotFound);
+
+    if (auto layer_ref = m_surface_flinger->FindLayer(layer->GetConsumerBinderId())) {
+        LOG_DEBUG(Service_VI, "called, SetLayerZIndex layer_id={} z={} (cid={})", layer_id,
+                 z_index, layer->GetConsumerBinderId());
+        layer_ref->z_index = z_index;
+    } else {
+        LOG_DEBUG(Service_VI, "called, SetLayerZIndex failed to find layer for layer_id={} (cid={})",
+                 layer_id, layer->GetConsumerBinderId());
+    }
+
+    R_SUCCEED();
+}
+
+Result Container::GetLayerZIndex(u64 layer_id, s32* out_z_index) {
+    std::scoped_lock lk{m_lock};
+
+    auto* const layer = m_layers.GetLayerById(layer_id);
+    R_UNLESS(layer != nullptr, VI::ResultNotFound);
+
+    if (auto layer_ref = m_surface_flinger->FindLayer(layer->GetConsumerBinderId())) {
+        *out_z_index = layer_ref->z_index;
+        R_SUCCEED();
+    }
+
+    R_RETURN(VI::ResultNotFound);
+}
+
 void Container::LinkVsyncEvent(u64 display_id, Event* event) {
     std::scoped_lock lk{m_lock};
     m_conductor->LinkVsyncEvent(display_id, event);