[fix] Fallback to string keys in maps

[ferozco]

Before this PR

We would generate key types by resolving the type of the key. This caused definitions with maps containing booleans and doubles as keys to generate invalid TypeScript.

After this PR

We fall back to string on any type which is not a string or an enum

[dansanduleac]

Currently, this still means that the double keys 0 and 0.0 will be different items in the map (since even the javascript equality on double values considers them different). There's not much we can do about that while javascript doesn't offer a meaningful equality relation.

However, once we finish defining the RFC for deduping map keys and set items we should add custom logic to dedupe keys correctly based on their conjure types.