[wrangler/d1] Support migrations in a directory (multi-file migrations)

[Ehbraheem]

Summary

Allow a migration to be either:

• a top-level .sql file (unchanged), or
• a directory whose name is the migration name and which contains one or more .sql files (executed in deterministic order).

• Tests
  • Tests included
  • Tests not necessary because:
• Public documentation
  • Cloudflare docs PR(s):
  • Documentation not necessary because: internal behavior change; README/docs follow-up can be added separately.
• Wrangler V3 Backport
  • Wrangler PR:
  • Not necessary because: change is contained to D1 migration logic and tests in this repo.

[changeset-bot]

🦋 Changeset detected

Latest commit: 83cbf7b

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 3 packages

Name	Type
wrangler	Patch
@cloudflare/vite-plugin	Patch
@cloudflare/vitest-pool-workers	Patch

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[Ehbraheem]

@penalosa, please help take a look at this PR when you're free.

This change will help unblock dev work