[next] Add EdgeRuntime provider environment variable to the builder

[Schniz]

This will enable Next.js to compile and set vercel as the edge runtime provider (EdgeRuntime global),
which can allow different libraries/customers to have different code running depends on the runtime environment (edge-runtime vs vercel).

Related Issues

• Upgrade edge-runtime + make EdgeRuntime value overridable with an env var on compilation next.js#38331

📋 Checklist

Tests

The Next.js feature was not merged yet, so it still can't be tested.

• The code changed/added as part of this PR has been covered with tests
• All tests pass locally with yarn test-unit

Code Review

• This PR has a concise title and thorough description useful to a reviewer
• Issue from task tracker has a link to this PR