[Themes] Feat: Poll for JSON changes when the `themeEditorSync` flag is passed to the `dev` command

[jamesmengo]

WHY are these changes introduced?

• Adds polling for https://github.com/Shopify/develop-advanced-edits/issues/203

WHAT is this pull request doing?

• Fetches checksums from the remote theme
• Performs reconciliations
• Schedules another call the fetch checksums after 3 seconds

How to test your changes?

1. pnpm shopify theme dev --path=<PATH_TO_THEME> --dev-preview --theme-editor-sync

Remote Changes -> should automatically propagate locally

---

deleting a file in your editor -> should delete locally modifying a file in your editor -> should update local theme creating a file in your editor -> should download locally

Local Changes (No-op)

---

delete/modify/create a file in your local theme -> do nothing (this will be handled by FS Watcher)

Remote + local Changes

---

delete/modify/create a file in your local theme that is also changed on remote -> Abort the entire process

https://github.com/Shopify/cli/assets/35415298/d5c1bb70-8c22-4c4d-ac87-5009d3a31fb0

Measuring impact

How do we know this change was effective? Please choose one:

• [ ] n/a - this doesn't need measurement, e.g. a linting rule or a bug-fix
• [x] Existing analytics will cater for this addition
• [ ] PR includes analytics changes to measure impact

Checklist

• [ ] I've considered possible cross-platform impacts (Mac, Linux, Windows)
• [x] I've considered possible documentation changes
• [x] I've made sure that any changes to dev or deploy have been reflected in the internal flowchart.