docs(alphabetical): document sort stability

Author: lislon

docs/array/alphabetical.mdx

@@ -11,6 +11,8 @@ the property to use for sorting, return a new array with the objects
 sorted alphabetically. A third, and optional, argument allows you to
 sort in descending order instead of the default ascending order.
 
+The function preserves the original order of items with equal values.
+
 For numerical sorting, see the [sort](./sort) function.
 
 ```ts

tests/array/alphabetical.test.ts

@@ -21,4 +21,9 @@ describe('alphabetical', () => {
     const result = _.alphabetical(cast(null), x => x)
     expect(result).toEqual([])
   })
+  test('sort is stable', () => {
+    const list = [{ id: 3, name: 'Leo' }, { id: 1, name: 'Leo' }, { id: 2, name: 'Leo' }]
+    const result = _.alphabetical(list, i => i.name)
+    expect(result).toEqual(list)
+  });
 })