A11y: Add types

[sirreal]

Description

Part of #18838
Extracted from #18942

Add types to a11y package.

Testing Instructions:

Verify type checking passes:

npm run lint-types

[sirreal]

This may be enough of an edge case that we could use a JSDoc cast:

Suggested change

	document.querySelector( 'body' )?.appendChild( container );
	/** @type { HTMLBodyElement } */ ( document.querySelector( 'body' ) ).appendChild( container );

The optional chain does seem to be correct, it's possible to have a document with no body:

document.createDocumentFragment().querySelector( 'body' ).appendChild( document.createElement( 'div' ) )
// Uncaught TypeError: Cannot read property 'appendChild' of null

That is an extreme edge case, however 🙂

[sirreal]

Whoops, I thought optional chaining was available already.

This change is blocked on #18939 or an alternative implementation.

[sirreal]

I removed the reassignment of the local variables which seems to serve no purpose here.

[sirreal]

Rebased and feedback addressed.

[sirreal]

This has some an issue with tsc runs:

packages/a11y/src/index.js:4:22 - error TS2307: Cannot find module '@wordpress/dom-ready'.

4 import domReady from '@wordpress/dom-ready';
                       ~~~~~~~~~~~~~~~~~~~~~~


Found 1 error.

We'll need to figure out how to make tsc aware of other packages, likely along the lines of #18838 (comment)

[sirreal]

This fixes the issues with the unfound @wordpress/dom-ready module and doesn't seem to introduce any issues.

Seems sufficient for now.

[aduth]

This fixes the issues with the unfound @wordpress/dom-ready module and doesn't seem to introduce any issues.

Seems sufficient for now.

Related: #18927

Once this is in place, we'll probably have trouble adding types to anything which depends on another package which isn't type-ready (i.e. if there are any errors in the dependency code).

[sirreal]

we'll probably have trouble adding types to anything which depends on another package which isn't type-ready

Based on my experience here, it's already a problem because tsc can't locate the modules.

[sirreal]

Would you prefer to sort that out in #18927 or shall we include it here and merge this?

[aduth]

Would you prefer to sort that out in #18927 or shall we include it here and merge this?

I've merged #18927 if you want to go ahead and rebase it here.

[sirreal]

I've rebased, this should be ready to land now.