Tooling: automated migration PRs

[43081j]

A thing we've had in the roadmap for a while now: automating migration PRs.

Imagine dependabot PRs but for things like:

• dropping redundant polyfills
• module replacements
• consolidation of dependencies duplicating functionality

From what I remember, renovate were open to collab on this (such that it ends up in renovate) but i think we're better off iterating quickly on our own GitHub action initially. once we have one that works, we can hopefully integrate into renovate too

Basic usage

• Run on a trigger
  • The user sets this up in their workflow (e.g. a schedule, weekly)
• Detect replaceable modules
  • The same way the CLI and ESLint plugin do
• Automatically migrate from these modules
  • User should be able to decide if we do all at once or one at a time (i.e. one PR per module)
  • Use the existing codemods repo
• Create a PR with this updated branch

Known gaps

Codemods are only replacements

The codemods we already have are for module replacements. We don't yet have any for removing packages like polyfills if I remember correctly.

Module replacements v2

We need module replacements v2 (tracking issue) since we need a way to detect engine constraints, especially for the polyfill removal stuff.