Facets - Display term count

[felipeelia]

Description of the Change

This PR adds a new toggle to both Facets blocks, so the user can display or not the term count in each facet. This PR also makes some small changes in the way one can get settings values from a feature:

• get_settings() now return default values as well
• A new get_setting() method was introduced

Closes #3286

How to test the Change

1. Create some facet blocks (taxonomy and meta)
2. Change the Display Term Count toggle to see it displaying or hiding the term count

Changelog Entry

Added - Option to display term counts in Facets blocks

Credits

Props @felipeelia

Checklist:

• I agree to follow this project's Code of Conduct.
• I have updated the documentation accordingly.
• I have added tests to cover my change.
• All new and existing tests pass.