feat(richtext-lexical): Blocks: generate type definitions for blocks fields

[AlessioGr]

Description

Closes #3993

This also now always sets unreachableDefinitions: true when generating types. This is because richText blocks types (e.g. from interfaceName prop) which are put in the definitions are currently not referenced anywhere.

In my opinion, these should still be included in the generated types in case the user wants to use them in their project, though.

• [X] I have read and understand the CONTRIBUTING.md document in this repository.

Type of change

• [ ] Chore (non-breaking change which does not add functionality)
• [ ] Bug fix (non-breaking change which fixes an issue)
• [X] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] Change to the templates directory (does not affect core functionality)
• [ ] Change to the examples directory (does not affect core functionality)
• [ ] This change requires a documentation update

Checklist:

• [ ] I have added tests that prove my fix is effective or that my feature works
• [ ] Existing test suite passes locally with my changes
• [ ] I have made corresponding changes to the documentation