Add an option to restrict user input within richText input

[simovicaleksa]

The problem

Currently you can filter the unwanted features within lexical editor by passing the editor object, containing a features array, to a richText field.

For example we can do something like this to create a rich text input in admin which will only have an option to insert a table. Problem is that this doesn't restrict the user from inserting text or breaks even if you just want a UI to manage a table or a heading for example (screenshot below showcasing the problem).

{
  name: "table",
  type: "richText",
  localized: true,
  editor: lexicalEditor({
    features: () => [
      EXPERIMENTAL_TableFeature(),
    ],
  }),
},

As you can see here, currently the only feature is a table, but the user is able to get away with inserting text making impossible to manage specific/expected content for things like tables or headings intuitive through current admin.

Suggestion

Introduce 2 new default features, TextFeature and BreakFeature, which when not included in the lexical editor config disable the users from creating non-intended formats of rich text.