feat: add experimental transition focus manager

Issue number: resolves #23650

What is the current behavior?

In traditional native applications, navigation will inform screen readers that the view has changed. This allows screen readers to focus the correct view. In a single page app on the web, this same concept does not exist. As a result, transitioning from Page A to Page B results in screen reader focus remaining on Page A. This means that users who rely on screen readers are not informed of view changes.

Currently, developers are responsible for implementing this on their own.

What is the new behavior?

Introduces a new focus manager priority global config. When defined, the app developer can specify which area of the view focus should be moved to when the transition ends. The developer does this by specifying areas in order of priority which allows for fallbacks in the event that a particular UI component (such as a header) does not exist on a view.

There is some risk here by managing focus for the application. As a result, this feature is considered experimental and disabled by default. The team should collect feedback based on usage and enable it by default when they feel this feature is stable enough.

Does this introduce a breaking change?

[ ] Yes
[x] No

Other information

⚠️ Due to the tsconfig.json change, reviewers should restart the Stencil dev server when checking out these changes locally.

Reviewers: Please test both of the test template files on physical iOS and Android device with VoiceOver and TalkBack enabled, respectively.

Docs Link: https://github.com/ionic-team/ionic-docs/pull/3627

ionic-team / ionic-framework