[test] Assert accessible name

[eps1lon]

Using https://github.com/eps1lon/dom-accessibility-api#dom-accessibility-api we add a custom matcher to make statements about the accessible name. This can be seen as the content that a screen reader will announce when the cursor is on the element.

The idea is that this will later be incorporated into ByRole. App tests will be written as getByRole('textbox', { name: 'foo' }) while the library test verifies that the rendered textbox does indeed have the accessible name (via aria-label or aria-labelledby or label element).

This will let us write better test that capture how the accessibility story of e.g. inputs looks. It is not obvious right now how to get this right and I don't want to rewrite a bunch of tests when we can improve the API and implementation later (see experimental useUniqueId or Scope).

Implementation notes:

• assuming visibility locally but verifying in CI i.e. getComputedStyle is faked locally

[eps1lon]

Don't get distracted with the role (it's unclear whether this is correct). Nvda properly announces this as a combobox.

The important part is that we have a test for the accessible name of a select. I'll add a test to the TextField as well and to check how native vs non-native behaves (which requires verification with nvda).

[mui-pr-bot]

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[eps1lon]

Now with less code and less whitespace