railties: Move the definition of PluginGenerator.app_path to railties.rbs

[tk0miya]

As a preparation of https://github.com/ruby/gem_rbs_collection/pull/693, this moves the definition of Rails::Generator::PluginGenerator#app_path to railties.rbs

[github-actions[bot]]

@tk0miya Thanks for your contribution!

Please follow the instructions below for each change. See also: https://github.com/ruby/gem_rbs_collection/blob/main/docs/CONTRIBUTING.md

Available commands

You can use the following commands by commenting on this PR.

• /merge: Merge this PR if CI passes

---

railties

You changed RBS files for an existing gem. You need to get approval from the reviewers of this gem.

@ksss, please review this pull request. If this change is acceptable, please make a review comment including APPROVE from here.

After that, the PR author or the reviewers can merge this PR. Just comment /merge to merge this PR.

[tk0miya]

ah, sorry. It's mistake... I'd like to do only moving Rails::Generator::PluginGenerator#app_path...

[tk0miya]

Now I busted zombies from #692.

[github-actions[bot]]

Thanks for your review, @ksss!

@tk0miya, @ksss This PR is ready to be merged. Just comment /merge to merge this PR.

[tk0miya]

/merge