Investigate impact of removing support for `@import` on prototypes

[romaricpascal]

What

Investigate which changes are needed in prototype if we remove support for @import in GOV.UK Frontend. Particularly:

• Can the Prototype Kit support both @import and @use in parallel
• Do we need to prepare training of some sorts around @use? Guidance maybe?
• Can the Prototype Kit share configuration between libraries that @use GOV.UK Frontend and @import GOV.UK Frontend
• Can our init.scss help us remove support for @import early on while other libraries keep using @import?

Why

To make upgrading prototypes to the version of GOV.UK Frontend that no longer supports @import as easy as possible for Prototype Kit users

Who needs to work on this

Developers

Who needs to review this

Developers

Done when

• We've investigating how the Prototype Kit would react to GOV.UK Frontend only supporting @use
• We have a plan for how to help Prototype Kit users when we remove support for @import in GOV.UK Frontend
• We've added issues on GitHub to implement the plan