Framework: Extract notices state from editor module

[aduth]

Notices are not an editor-specific feature, yet the current notices state lives within editor. Before plugins start integrating more with this functionality, we should consider whether to extract it, either to its own module (like viewport), or to components, or perhaps even to a new concept of "data-bound components".

See also #5316 which highlights some issues with the viewport approach of independent data modules exporting their own components, as it can result in circular dependencies between components and the individual module.

Proposal options:

• Create new notices folder, which creates its own data state
  • Either exposes a data-bound component which editor uses to render, or this component lives elswhere
• Add new notices component to components directory, which bundles its own data state

Open questions:

Do we need concepts of scoped notices? If a plugin adds a notice and intends for it to be shown in the editor, how does this scale out to a more general solution? Is this something we need to address now?

[danielbachhuber]

Some relevant prior issues:

• Introduce formal API for displaying notices #5975 Introduce formal API for displaying notices
• Capture admin notices and summarize them in editor #5590 Capture admin notices and summarize them in editor

[collimarco]

This issue has been closed, but traditional admin_notices don't work in Gutenberg (they are not displayed...)

Please fix this