Expose color selection method

[jacekbogdanski]

Type of report

Feature request

Provide description of the new feature

Color Button plugin has a private function allowing to select a chosen color from the panel block. With the addition of #3727 feature, it makes sense to expose this function, so it's possible to intercept color command and provide custom color choosing scenarios for more advanced features like Spreadsheets. Preferably, exposed API should be straightforward, similar to #3387

var ui = editor.ui.get( 'TextColor' ); // For background color use BGColor instead.
ui.select( function( item ) {
  return item.value === '#fafafa';
} );

Note that this feature should only handle colors from the color button panel as colors from the color dialog are not preserved in UI yet.

[jacekbogdanski]

Also, it would be good to have some option to select auto color if a color has not been found. It may be the default behavior of the selection method.