Fix(Generate): generate Dropdown before container

[stonebuzz]

Checklist before requesting a review

Please delete options that are not relevant.

• I have performed a self-review of my code.
• I have added tests (when available) that prove my fix is effective or that my feature works.
• This change requires a documentation update.

Description

• It fixes Regenerate stops working once a block has been created on a Custom Fields associated type #860

This PR adjusts the file regeneration process created by fields.
From now on, the files will be generated in two steps:

• Generation of files related to dropdowns.
• Generation of files related to containers.

This prevents a fatal error when a container is added to a dropdown created in another container (and not yet generated).

Screenshots (if appropriate):

[trasher]

LGTM if fix is confirmed by reporter