Add (unfinished) SDL_iostream.inc

Adds just one type (PSDL_IOStream) needed for surface support

Author: Free-Pascal-meets-SDL-Website

units/SDL_iostream.inc

@@ -0,0 +1,22 @@
+{
+  This file is part of:
+
+    SDL3 for Pascal
+    (https://github.com/PascalGameDevelopment/SDL3-for-Pascal)
+    SPDX-License-Identifier: Zlib
+}
+
+{*
+ * The read/write operation structure.
+ *
+ * This operates as an opaque handle. There are several APIs to create various
+ * types of I/O streams, or an app can supply an SDL_IOStreamInterface to
+ * SDL_OpenIO() to provide their own stream implementation behind this
+ * struct's abstract interface.
+ *
+ * \since This struct is available since SDL 3.1.3.
+  }
+type
+  PPSDL_IOStream = ^PSDL_IOStream;
+  PSDL_IOStream = type Pointer;
+