[cpp] More func comparisons

[Aidan63]

Fixes #12872

There were two problems.

1. Class function closures should not be compared based on their signature, but they were. These closures now override callableId which means they no longer return an Id representing the signature.
2. On the hxcpp side when callables are "wrapped" due to the signature changing I forgot to have these wrapped callables override callableId which meant they weren't returning the Id of the underlying callable.

The hxcpp side will need to be merged in before the new tests pass for cpp.

HaxeFoundation/hxcpp#1337