Make ClearPlatformHandlers and ClearRendererHandlers API public (#9016)

Author: irieger

imgui.h

@@ -3978,8 +3978,8 @@ struct ImGuiPlatformIO
     // Functions
     //------------------------------------------------------------------
 
-    void    ClearPlatformHandlers();    // Clear all Platform_XXX fields. Typically called on Platform Backend shutdown.
-    void    ClearRendererHandlers();    // Clear all Renderer_XXX fields. Typically called on Renderer Backend shutdown.
+    IMGUI_API void ClearPlatformHandlers();    // Clear all Platform_XXX fields. Typically called on Platform Backend shutdown.
+    IMGUI_API void ClearRendererHandlers();    // Clear all Renderer_XXX fields. Typically called on Renderer Backend shutdown.
 };
 
 // (Optional) Support for IME (Input Method Editor) via the platform_io.Platform_SetImeDataFn() function. Handler is called during EndFrame().