Fix comparison for arrays (#208171)

The comparison helper is not considering arrays - this means when
comparing two objects with arrays, it will always find a diff because to
the `!==` operator, the arrays are not the same:
```ts
calculateObjectDiff(
 { alpha: [1, 2, 3], beta: [4, 5, 6] },
 { alpha: [1, 2, 3], beta: [4, 5, 6] })
```

This PR fixes this by recursing into each element of the array.

src/platform/packages/shared/kbn-object-utils/src/calculate_object_diff.test.ts

@@ -40,4 +40,34 @@ describe('calculateObjectDiff', () => {
     expect(removed).toEqual({});
     expect(updated).toEqual({});
   });
+
+  it('should handle array fields correctly', () => {
+    const { added, removed, updated } = calculateObjectDiff(
+      { alpha: [1, 2, 3], beta: [4, 5, 6] },
+      { alpha: [1, 2, 3], beta: [4, 5, 7] }
+    );
+    expect(added).toEqual({});
+    expect(removed).toEqual({});
+    expect(updated).toEqual({ beta: [undefined, undefined, 7] });
+  });
+
+  it('should detect added and removed array fields', () => {
+    const { added, removed, updated } = calculateObjectDiff(
+      { alpha: [1, 2, 3] },
+      { beta: [4, 5, 6] }
+    );
+    expect(added).toEqual({ beta: [4, 5, 6] });
+    expect(removed).toEqual({ alpha: [1, 2, 3] });
+    expect(updated).toEqual({});
+  });
+
+  it('should handle arrays containing objects correctly', () => {
+    const { added, removed, updated } = calculateObjectDiff(
+      { alpha: [{ beta: 1 }, { gamma: 2 }] },
+      { alpha: [{ beta: 1 }, { gamma: 3 }] }
+    );
+    expect(added).toEqual({});
+    expect(removed).toEqual({});
+    expect(updated).toEqual({ alpha: [{}, { gamma: 3 }] });
+  });
 });

src/platform/packages/shared/kbn-object-utils/src/calculate_object_diff.ts

@@ -27,6 +27,10 @@ interface ObjectDiffResult<TBase, TCompare> {
   };
 }
 
+function isAllUndefined(obj: unknown): boolean {
+  return Array.isArray(obj) && obj.every((value) => value === undefined);
+}
+
 /**
  * Compares two JSON objects and calculates the added and removed properties, including nested properties.
  * @param oldObj - The base object.
@@ -66,6 +70,20 @@ export function calculateObjectDiff<TBase extends Obj, TCompare extends Obj>(
         );
         if (isEmpty(addedMap[key])) delete addedMap[key];
         if (isEmpty(removedMap[key])) delete removedMap[key];
+      } else if (Array.isArray(base[key]) && Array.isArray(compare[key])) {
+        addedMap[key] = [];
+        removedMap[key] = [];
+        updatedMap[key] = [];
+        diffRecursive(
+          base[key] as Obj,
+          compare[key] as Obj,
+          addedMap[key] as Obj,
+          removedMap[key] as Obj,
+          updatedMap[key] as Obj
+        );
+        if (isAllUndefined(addedMap[key])) delete addedMap[key];
+        if (isAllUndefined(removedMap[key])) delete removedMap[key];
+        if (isAllUndefined(updatedMap[key])) delete updatedMap[key];
       } else if (base[key] !== compare[key]) {
         updatedMap[key] = compare[key];
       }