Support SDL_EVENT_DROP_FILE in Windows with IDropTarget instead of WM_DROPFILES

Support SDL_EVENT_DROP_TEXT in Windows

  src/video/windows/SDL_windowsvideo.c + .h
    Connect      to COM WIN_CoInitialize   + OLE OleInitialize   in WIN_VideoInit
    Disconnect from COM WIN_CoUninitialize + OLE OleUninitialize in WIN_VideoQuit
  src/video/windows/SDL_windowswindow.c + .h
    Create / Destroy IDropTarget or use fallback WM_DROPFILES
      depending on OleInitialize success in WIN_VideoInit
    Handle text/uri-list, text/plain;charset=utf-8, CF_UNICODE_TEXT, CF_TEXT, CF_HDROP
    Call terminating WIN_AcceptDragAndDrop from WIN_DestroyWindow ( CleanupVideoData )

src/video/windows/SDL_windowsvideo.c

@@ -467,6 +467,21 @@ static void WIN_InitDPIAwareness(SDL_VideoDevice *_this)
 int WIN_VideoInit(SDL_VideoDevice *_this)
 {
     SDL_VideoData *data = _this->internal;
+    HRESULT hr;
+
+    hr = WIN_CoInitialize();
+    if (SUCCEEDED(hr)) {
+        data->coinitialized = SDL_TRUE;
+
+        hr = OleInitialize(NULL);
+        if (SUCCEEDED(hr)) {
+            data->oleinitialized = SDL_TRUE;
+        } else {
+            SDL_LogInfo(SDL_LOG_CATEGORY_VIDEO, "OleInitialize() failed: 0x%.8x, using fallback drag-n-drop functionality\n", (unsigned int)hr);
+        }
+    } else {
+        SDL_LogInfo(SDL_LOG_CATEGORY_VIDEO, "CoInitialize() failed: 0x%.8x, using fallback drag-n-drop functionality\n", (unsigned int)hr);
+    }
 
     WIN_InitDPIAwareness(_this);
 
@@ -511,6 +526,8 @@ int WIN_VideoInit(SDL_VideoDevice *_this)
 
 void WIN_VideoQuit(SDL_VideoDevice *_this)
 {
+    SDL_VideoData *data = _this->internal;
+
 #if !defined(SDL_PLATFORM_XBOXONE) && !defined(SDL_PLATFORM_XBOXSERIES)
     WIN_QuitModes(_this);
     WIN_QuitDeviceNotification();
@@ -525,6 +542,15 @@ void WIN_VideoQuit(SDL_VideoDevice *_this)
 
     WIN_SetRawMouseEnabled(_this, SDL_FALSE);
     WIN_SetRawKeyboardEnabled(_this, SDL_FALSE);
+
+    if (data->oleinitialized) {
+        OleUninitialize();
+        data->oleinitialized = SDL_FALSE;
+    }
+    if (data->coinitialized) {
+        WIN_CoUninitialize();
+        data->coinitialized = SDL_FALSE;
+    }
 }
 
 #if !defined(SDL_PLATFORM_XBOXONE) && !defined(SDL_PLATFORM_XBOXSERIES)

src/video/windows/SDL_windowsvideo.h

@@ -379,6 +379,9 @@ struct SDL_VideoData
 {
     int render;
 
+    SDL_bool coinitialized;
+    SDL_bool oleinitialized;
+
     DWORD clipboard_count;
 
 #if !defined(SDL_PLATFORM_XBOXONE) && !defined(SDL_PLATFORM_XBOXSERIES) /* Xbox doesn't support user32/shcore*/

src/video/windows/SDL_windowswindow.h

@@ -48,6 +48,16 @@ typedef enum SDL_WindowEraseBackgroundMode
     SDL_ERASEBACKGROUNDMODE_ALWAYS,
 } SDL_WindowEraseBackgroundMode;
 
+typedef struct
+{
+    void **lpVtbl;
+    int refcount;
+    SDL_Window *window;
+    HWND hwnd;
+    UINT format_text;
+    UINT format_file;
+} SDLDropTarget;
+
 struct SDL_WindowData
 {
     SDL_Window *window;
@@ -89,6 +99,7 @@ struct SDL_WindowData
 
     /* Whether we retain the content of the window when changing state */
     UINT copybits_flag;
+    SDLDropTarget *drop_target;
 };
 
 extern int WIN_CreateWindow(SDL_VideoDevice *_this, SDL_Window *window, SDL_PropertiesID create_props);