Refactor Renderer access and improve gesture handling in iOS and test files

- Replaced instances of Renderer::GetInstance() with Renderer::Get() for consistency across the codebase.
- Enhanced gesture handling in iOS by adding mouse position events for touch gestures.
- Streamlined test initialization for ImGui to align with recent renderer access changes.

src/app/emu/emulator.cc

@@ -49,7 +49,7 @@ using ImGui::Text;
 void Emulator::Run() {
   static bool loaded = false;
   if (!snes_.running() && rom()->is_loaded()) {
-    ppu_texture_ = SDL_CreateTexture(core::Renderer::GetInstance().renderer(),
+    ppu_texture_ = SDL_CreateTexture(core::Renderer::Get().renderer(),
                                      SDL_PIXELFORMAT_ARGB8888,
                                      SDL_TEXTUREACCESS_STREAMING, 512, 480);
     if (ppu_texture_ == NULL) {