Full Site Editing: Replace save buttons with temporary attribute changes [1]

[glendaviesnz]

Currently the Site Description and Site Title FSE blocks have their own save buttons, as changes to these blocks do not update the editor dirty state.

After discussion at paAmJe-tF-p2 about better solutions to this it was decided to remove the save buttons on both of these blocks and instead use a temporary attribute value that can be updated on changes in order to indicate dirty state to the editor.

Example implementation.

This is a temporary fix to this issue while the generalisation of custom sources is worked on in the core editor (WordPress/gutenberg#16075) and the subsequent adding of a site options source as a more permanent solution.