Components: Notice: Handle spoken message from component, not store #15708

Previously: https://github.com/WordPress/gutenberg/pull/15594/files#r284613950

Currently, it is the responsibility of the notices store to emit the spoken message when a notice is created. While this ensures that any notice which operates via the createNotice store action will be spoken, it misses messages which may be displayed by using the Notice component directly. If it's agreeable that a spoken message be considered as a necessary element of the displayed notice, it would therefore make sense to migrate this out of the data store and instead implemented as an effect of the component.

Implementation notes:

Remove SPEAK control yielding and control handler:

Implement instead as part of lifecycle of the component:

https://github.com/WordPress/gutenberg/blob/master/packages/components/src/notice/index.js

Likely using useEffect to emulate componentDidMount and componentDidUpdate:

https://reactjs.org/docs/hooks-effect.html

If #15594 is merged, it adds additional consideration for polite and assertive spoken messages. This should be handled instead from the Notice and Snackbar components.