SDLControllerInterface: Add support for optional game controller database

If an optional "gamecontrollerdb.txt" file exists in the user directory,
then SDL game controller mappings will be loaded from it.

There is an officially endorsed community sourced database in
https://github.com/gabomdq/SDL_GameControllerDB

src/frontend-common/sdl_controller_interface.cpp

@@ -1,5 +1,6 @@
 #include "sdl_controller_interface.h"
 #include "common/assert.h"
+#include "common/file_system.h"
 #include "common/log.h"
 #include "core/controller.h"
 #include "core/host_interface.h"
@@ -23,6 +24,17 @@ bool SDLControllerInterface::Initialize(CommonHostInterface* host_interface)
 
   FrontendCommon::EnsureSDLInitialized();
 
+  const std::string gcdb_file_name = GetGameControllerDBFileName();
+  if (FileSystem::FileExists(gcdb_file_name.c_str()))
+  {
+    Log_InfoPrintf("Loading game controller mappings from '%s'", gcdb_file_name.c_str());
+    if (SDL_GameControllerAddMappingsFromFile(gcdb_file_name.c_str()) < 0)
+    {
+      Log_ErrorPrintf("SDL_GameControllerAddMappingsFromFile(%s) failed: %s",
+                      gcdb_file_name.c_str(), SDL_GetError());
+    }
+  }
+
   if (SDL_InitSubSystem(SDL_INIT_JOYSTICK | SDL_INIT_GAMECONTROLLER | SDL_INIT_HAPTIC) < 0)
   {
     Log_ErrorPrintf("SDL_InitSubSystem(SDL_INIT_JOYSTICK |SDL_INIT_GAMECONTROLLER | SDL_INIT_HAPTIC) failed");
@@ -48,6 +60,11 @@ void SDLControllerInterface::Shutdown()
   ControllerInterface::Shutdown();
 }
 
+std::string SDLControllerInterface::GetGameControllerDBFileName() const
+{
+  return m_host_interface->GetUserDirectoryRelativePath("gamecontrollerdb.txt");
+}
+
 void SDLControllerInterface::PollEvents()
 {
   for (;;)

src/frontend-common/sdl_controller_interface.h

@@ -17,6 +17,9 @@ public:
   bool Initialize(CommonHostInterface* host_interface) override;
   void Shutdown() override;
 
+  /// Returns the path of the optional game controller database file.
+  std::string GetGameControllerDBFileName() const;
+
   // Removes all bindings. Call before setting new bindings.
   void ClearBindings() override;