Refactor: split up maybe_hoist_and_create_proxy (and cache variant)

The functions `maybe_hoist_and_create_proxy` and
`maybe_hoist_and_create_proxy_to_cache` are currently declared to accept
an optional function declaration and/or an optional arrow function
expression. Most of their implementation is then forked on whether
either of those is passed in.

However, all call sites always pass in either a well-defined function
declaration or a well-defined arrow function expression, never both and
never none. Therefore it makes sense to split up those functions, and
avoid declaring the params and return types with `Option`.