Check optional fields (may be present in object or not)

## Description

I have a case when the field can be present or not in the object. I would like to check the field if it's present in the object
Case 1: `{ a: 10, b: 'qwerty' }`
Case 2: `{ a: 10, b: 'qwerty' , c: 10}`

(this won't work)
```typescript
expect({ a: 10, b: 'qwerty' }).toMatchObject({
a: expect.toBePositiveNumber(),
b: expect.toBeNonEmptyString(),
c: expect.toBeOptionalOf(expect.toBeNumber()),
})
```

Returns error:
```
Expected: {"a": toBePositiveNumber<>, "b": toBeNonEmptyString<>, "c": toBeOptionalOf}
Received: {"a": 10, "b": "qwerty"}

```
Maybe there is a way to check **optional** field?

## Suggested Solution

## Help Needed

Start at the TypeScript matcher entry points named in the example, toMatchObject and toBeOptionalOf, and inspect the existing matcher tests; no test file is identified in the issue. Done means an absent c field is accepted while a present c field is validated, without changing the required checks for a and b.

Written by the indexing model from the issue text.