Fix bug causing intermittent GUI unit test failures (#11801)

Fix failing prop test caused by edge case bug in new `findDifferenceIndex`.

Author: kazcw

app/gui/src/project-view/util/__tests__/array.test.ts

@@ -42,7 +42,7 @@ test.prop({
 test.prop({
   array: fc.array(fc.anything()),
 })('findDifferenceIndex (same array)', ({ array }) => {
-  expect(findDifferenceIndex(array, array)).toEqual(array.length)
+  expect(findDifferenceIndex(array, array, Object.is)).toEqual(array.length)
 })
 
 test.prop({
@@ -69,3 +69,8 @@ test.prop({
     expect(arr1[differenceIndex]).not.toEqual(arr2[differenceIndex])
   }
 })
+
+test('findDifferenceIndex (NaN)', () => {
+  const array = [NaN]
+  expect(findDifferenceIndex(array, array)).toEqual(0)
+})

app/gui/src/project-view/util/data/array.ts

@@ -90,7 +90,8 @@ export function partition<T>(array: Iterable<T>, pred: (elem: T) => boolean): [T
 }
 
 /**
- * Find smallest index at which two arrays differ. Returns an index past the array (i.e. array length) when both arrays are equal.
+ * Find smallest index at which two arrays differ. Returns an index past the array (i.e. array length) when both arrays
+ * are equal. Note that the default comparator uses strict equality, and so `NaN` values will be considered different.
  */
 export function findDifferenceIndex<T>(
   lhs: T[],