[build-utils][frameworks] Add support for runtime properties

[styfle]

This PR adds two properties to frameworks.json:

1. useRuntime - this moves the special case for non @vercel/static-build frontends, so that any framework can do the same as Next.js and RedwoodJS
2. ignoreRuntimes - this allows a framework to opt out of api detection such as RedwoodJS which handle's its own .js extensions

This also fixes 2 bugs discovered during implementing the feature:

1. test-unit.yml was not testing Node 12, it was testing 10 for both runs
2. sortFilesBySegmentCount() was non-deterministic causing node 10 and 12 to sort differently