The 'prototype' prop of a source function is, by default, an empty object with
a 'constructor' prop pointing back to the function. Currently, every source
function is created in this fashion, which makes it a circular reference
and thus prevents it from being freed until the Garbage Collector kicks in.

The performance impact comes from the function keeping a ref to the
enclosing scope, and since the scope is being held by it, the engine will
detach the scope, believing it to be used for the time being (until the
GC cleans it). This can cause substantial performance issues for such a
common case. The FFXIV Launcher, for example, leaks a large amount of such
short-lived functions and the enclosing scopes.
Signed-off-by: Gabriel Ivăncescu <gabrielopcode@gmail.com>