toHaveSelectionValue

### Describe the feature you'd like:

I'm testing a combobox element with a behavior that is quite similar to the address bar in the browser. That is, when you start typing, it automatically completes the text with the first suggestion and highlights the completion string.

I would like to test this selection behavior.

### Suggested implementation:

```js
function toHaveSelectionValue(element, value) {
  const { selectionStart, selectionEnd } = element;
  const selectionValue = element.value.slice(selectionStart, selectionEnd);
  return {
    pass: selectionValue === value,
    ...
  };
}
```

### Describe alternatives you've considered:

I can check the `selectionStart` and `selectionEnd` properties on the `HTMLInputElement`, but this is not as easy to read. And I also have to explicitly cast the element if I'm using TypeScript.

```js
const input = getByLabelText("Fruits") as HTMLInputElement;
// Expect "pple" to be selected in "Apple"
expect(input.selectionStart).toBe(1);
expect(input.selectionEnd).toBe(5);
```

So, for now, I'm using an `expectSelectionValue` util function in my app.

### Teachability, Documentation, Adoption, Migration Strategy:

### `toHaveSelectionValue`

```js
toHaveSelectionValue(value: string)
```

This allows you to check whether the given textbox element has the specified selected (highlighted) value. It accepts `<input type="text">` and `<textarea>` elements.

#### Examples

```html
<input type="text" value="text" data-testid="input" />
```

##### Using DOM Testing Library

```js
const input = getByTestId('input')

input.setSelectionRange(1, 3)

expect(input).toHaveSelectionValue('ex')
```

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toHaveSelectionValue #289

Describe the feature you'd like:

Suggested implementation:

Describe alternatives you've considered:

Teachability, Documentation, Adoption, Migration Strategy: