Checklist

• I've run bundle exec rspec from the root directory to see all new and existing tests pass
• I've followed the fastlane code style and run bundle exec rubocop -a to ensure the code style is valid
• I've read the Contribution Guidelines
• I've updated the documentation if necessary.

Motivation and Context

This builds on top of #20293

We wish to replace import_from_git with this new action to use gem files to package the shared Fastfile and its dependencies. Together with the transitive dependencies it simplifies the use of a shared Fastfile.

We modify our repository containing our shared Gemfile by

• replacing our shared repo's Gemfile by a gemspec
• moving all Plugins into the gemspec file
• replacing the fastlane_version "x.y.z" in the shared Fastfile with a proper version constraint in the gemspec. For consumer projects, bundler will resolve the right dependency when needed

For our consumer projects this gives the following results:

• the project's gemfile contains a single dependency to the shared Gem (instead of one

gem 'name_of_gem', git: 'URL_GIT_REPO'

• we remove from the Pluginfile all dependencies now managed by bundler
• we replace our Fastfile import from

import_from_git(url: "URL_GIT_REPO", dependencies: [...])

to

import_from_gem(gem_name: "name_of_gem")

Extra benefits: builds are now reproducible. Updating the shared fastfile requires doing an update in the corresponding user projects.

I am opening this for discussion and can clean the code, add tests as needed.

Who can provide some feedback on this? @joshdholtz maybe?

Description

Testing Steps