Stricter ESM function-style rule detection

[bmish]

We currently look for:

• module.exports = function (context) { ... }
• export default function (context) { ... }

We could look for a default-exported function that has at least one object return:

• module.exports = function (context) { return { ... } }
• export default function (context) { return { ... } }

This would help reduce false positives.

Originally posted by @bmish in #201 (comment)

[bmish]

@aladdin-add I'll give this a try today.