chore: update sourcemaps of distributed JS plugins

chore: update sourcemaps of distributed JS plugins

Sourcemaps for distribution main files and build JS plugins were added in https://github.com/zurb/foundation-sites/pull/11012 but distribution JS plugins were forgotten. This commit change the `deploy:plugins` gulp task to generate and copy sourcemaps for JS plugin alongside their source files.

Changes:
* Split `deploy:plugins` into `deploy:plugins:sources` and `deploy:plugins:sourcemaps`
* Generate sourcemaps for minified plugins in `deploy:plugins:sources`
* Copy sourcemaps for plugins to dist folder in `deploy:plugins:sourcemaps`