Fix gradio-app#10764: Prevent automatic sorting of labels in gr.NativePlot components

Originally, the bug appeared to be isolated to
gr.BarPlot, but it turns out that it affects all
gr.NativePlot components including BarPlot,
LinePlot, and ScatterPlot.

Although the data does not seem sorted in the
program's flow, it gets sorted when the Svelte
file is rendered. This issue occurs because the
reformat_sort function in index.svelte of
nativeplot returns undefined when sort is null,
which, after compilation, is treated as void 0.
This implicitly triggers default sorting. To solve
this, I changed undefined to null, ensuring that
the compiled code handles it as null, resulting in
unsorted data being displayed in the browser.

Author: Rafalex04

js/nativeplot/Index.svelte

@@ -56,6 +56,7 @@
 		| "descending"
 		| { field: string; order: "ascending" | "descending" }
 		| string[]
+		| null
 		| undefined {
 		if (_sort === "x") {
 			return "ascending";
@@ -66,7 +67,7 @@
 		} else if (_sort === "-y") {
 			return { field: y, order: "descending" };
 		} else if (_sort === null) {
-			return undefined;
+			return null;
 		} else if (Array.isArray(_sort)) {
 			return _sort;
 		}