fix(docsearch-react): accessibility improvements

[isner]

These changes address some of the concerns raised in #1370.

Issues addressed:

• Incorrect role/attributes on dialog
• Focus lost/not managed when closing dialog
• Low-contrast text

Issues not addressed:

• Adding aria-hidden or inert to the elements underlying the modal dialog (this was a heavier lift than I was prepared to undertake, and adding the aria-modal="true" attribute to the dialog has addressed this issue for some ATs)
• Incorrect role/attributes on the search input itself (I don't think the input should actually be a combobox as suggested in Accessibility issues with v3 dialog #1370, since its purpose is not to assist the user in completing the field, but rather producing a list of navigation links)
• Low-contrast icons (I wasn't prepared to create new icons)

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[isner]

The Netlify deployment was cancelled automatically due to lack of content changes. This PR does introduce changes to the UI behavior and markup, however, so a preview deployment would still be useful. Is there any way to manually deploy from this branch?

[shortcuts]

Hey, thanks for the contribution 💙, I'll take a look at it ASAP!

a preview deployment would still be useful. Is there any way to manually deploy from this branch?

Indeed, you can update this line to include packages/docsearch-react too!

[isner]

a preview deployment would still be useful. Is there any way to manually deploy from this branch?

Indeed, you can update this line to include packages/docsearch-react too!

I made the change you requested, but I didn't realize that Netlify was only being used to deploy the DocSearch website. I don't think it's necessary to trigger a preview deployment of the website when the contents of the docsearch-react package are changed.

Instead, it would be useful to preview the changes that are introduced by this PR in CodeSandbox. When I follow the link provided by the codesandbox-ci bot I see the build output, which is great, but it's unclear how to access a working preview of that package build. This would be the easiest way for you to review the PR changes in action. Any suggestions?

[jfgreffier]

@isner @shortcuts this PR is from last year, is it still revelant ? If so, it probably needs a git rebase and solving the conflicts