Include symbol keys when diffing objects

As a result of jestjs#13639, `expect.toMatchObject` can now compare symbol keys.  However, the diffs that it generates if a symbol key doesn't match are misleading.  For example, the following assertion:

```
const Foo = Symbol("foo");
test("mismatched symbols", () => {
  expect({ a: 1, [Foo]: {id: 1} }).toMatchObject({ a: 1, [Foo]: {id: 2} });
});
```

fails as desired, but it displays the following diff:

```
    - Expected  - 3
    + Received  + 0

      Object {
        "a": 1,
    -   Symbol(foo): Object {
    -     "id": 2,
    -   },
      }
```

*Note*: In inspecting the code, I wonder if `getObjectSubset` should use the same logic as `subsetEquality` - i.e., if `subsetEquality` does not evaluate an object's inherited string keys when determining equality, then `getObjectSubset` should not evaluate an object's inherited string keys for reporting on inequality? To put it another way - jestjs#13639 appears to change `subsetEquality` from considering an object's inherited string keys to not considering inherited string keys, and I'm not sure if that was intentional in a SemVer-minor change.  For now, I've preserved the previous behavior, but let me know if this should change.

Fixes jestjs#13809

packages/expect-utils/src/utils.ts

@@ -43,6 +43,17 @@ const hasPropertyInObject = (object: object, key: string | symbol): boolean => {
   );
 };
 
+// Retrieves an object's keys for evaluation by getObjectSubset.  This evaluates
+// the prototype chain for string keys but not for symbols.  (Otherwise, it
+// could find values such as a Set or Map's Symbol.toStringTag, with unexpected
+// results.)
+//
+// Compare with subsetEquality's use of Reflect.ownKeys.
+const getObjectKeys = (object: object) => [
+  ...Object.keys(object),
+  ...Object.getOwnPropertySymbols(object),
+];
+
 export const getPath = (
   object: Record<string, any>,
   propertyPath: string | Array<string>,
@@ -131,7 +142,7 @@ export const getObjectSubset = (
     const trimmed: any = {};
     seenReferences.set(object, trimmed);
 
-    Object.keys(object)
+    getObjectKeys(object)
       .filter(key => hasPropertyInObject(subset, key))
       .forEach(key => {
         trimmed[key] = seenReferences.has(object[key])
@@ -144,7 +155,7 @@ export const getObjectSubset = (
             );
       });
 
-    if (Object.keys(trimmed).length > 0) {
+    if (getObjectKeys(trimmed).length > 0) {
       return trimmed;
     }
   }

packages/expect/src/__tests__/__snapshots__/matchers.test.js.snap

@@ -4140,13 +4140,13 @@ exports[`toMatchObject() {pass: false} expect({"a": "a", "c": "d"}).toMatchObjec
 exports[`toMatchObject() {pass: false} expect({"a": "b", "c": "d", Symbol(jest): "jest"}).toMatchObject({"a": "c", Symbol(jest): Any<String>}) 1`] = `
 <d>expect(</><r>received</><d>).</>toMatchObject<d>(</><g>expected</><d>)</>
 
-<g>- Expected  - 2</>
+<g>- Expected  - 1</>
 <r>+ Received  + 1</>
 
 <d>  Object {</>
 <g>-   "a": "c",</>
-<g>-   Symbol(jest): Any<String>,</>
 <r>+   "a": "b",</>
+<d>    Symbol(jest): Any<String>,</>
 <d>  }</>
 `;