feat(api): use uintptr_t instead of intptr_t for pointers (#265)

Image methods now accept the `long` type instead of `int`,
as they are expected to work with pointers as well.

imgui-binding/src/main/java/imgui/internal/ImGuiDockNode.java

@@ -61,7 +61,7 @@ public final class ImGuiDockNode extends ImGuiStruct {
     }
 
     private native long nGetChildNodeFirst(); /*
-        return (intptr_t)THIS->ChildNodes[0];
+        return (uintptr_t)THIS->ChildNodes[0];
     */
 
     /**
@@ -83,7 +83,7 @@ public final class ImGuiDockNode extends ImGuiStruct {
     }
 
     private native long nGetChildNodeSecond(); /*
-        return (intptr_t)THIS->ChildNodes[1];
+        return (uintptr_t)THIS->ChildNodes[1];
     */
 
     /**