Add initial ts setup for libsquoosh

Convert `image_data` to typescript as an example

libsquoosh/src/image_data.ts

@@ -0,0 +1,11 @@
+export default class ImageData {
+  readonly data: Uint8ClampedArray;
+  readonly width: number;
+  readonly height: number;
+
+  constructor(data: Uint8ClampedArray, width: number, height: number) {
+    this.data = data;
+    this.width = width;
+    this.height = height;
+  }
+}