feat: add support for alt text queries

[deecewan]

Summary

<Image /> has an alt prop, and this is what the screen reader uses to describe the image. There was previously no way to match on the alt text.

I've added matchers for alt text in this PR, so that we can find images using something accessible by screen readers.

Test plan

automated tests are included. these are based on the test-id tests.

[mdjastrzebski]

Hi @deecewan, thanks for submitting this PR.

I've done some initial checks, and it seems that alt and aria-label/accessibilityLabel are closely related:

• https://github.com/facebook/react-native/blob/8dabed60f456e76a9e53273b601446f34de41fb5/packages/react-native/Libraries/Image/Image.ios.js#L173
• https://github.com/facebook/react-native/blob/8dabed60f456e76a9e53273b601446f34de41fb5/packages/react-native/Libraries/Image/Image.android.js#L188

As far as I understand, this means that having alt or aria-label/accessibilityLabel + accessible props in runtime in indistinguishable. The same should be reflected in our queries and matchers.

Since thee above code is platform-specific code, not rendered in your snapshot tests, we would have to simulate that behavior.

In order to have proper support for querying images we would have to do following pieces:

• getByRole query to support querying images using getRole('image' | 'img', { name: altText });
• toHaveAccessibleName support checking alt text

As for getByAltText it should inspect alt props as now, but it should also match when all of the following conditions are met:

• view is a host image
• accessible prop is set
• aria-label/accessibilityLabel matches expected alt text

I am still on the fence for adding *ByAltText matcher as on one hand it increases RTL compatibility but on the other hand is ok but not really recommended way to query things in RLT (see query priorities, KCD advice) and has not be request for so far by the users (you're first).

@deecewan would you be willing to submit a separate PR for Image alt prop support in existing queries (byRole) and matchers (toHaveAccessibleName) as described above? In the mean time we can discuss whether to include ByAltText matcher.

[mdjastrzebski]

Closing as #1663 seems to provide the required functionality without expanding API surface.