Route render capture hooks through platform services

src/app.cpp

@@ -16,10 +16,7 @@
 #endif
 #include "settings.h"
 
-#ifdef _WIN32
-void win32_renderdoc_frame_start();
-void win32_renderdoc_frame_end();
-#elif __LINUX__
+#ifdef __LINUX__
 std::string linux_home_path();
 int mkpath(const std::string& dir, mode_t mode = DEFFILEMODE);
 #elif __WEB__
@@ -818,16 +815,12 @@ std::string App::res_to_string(int res)
 
 void App::renderdoc_frame_start()
 {
-#if __WIN__
-    win32_renderdoc_frame_start();
-#endif
+    begin_render_capture_frame();
 }
 
 void App::renderdoc_frame_end()
 {
-#if __WIN__
-    win32_renderdoc_frame_end();
-#endif
+    end_render_capture_frame();
 }
 
 void App::rec_clear()