Improve IType::Record type

[mikevoronov]

At the moment IType::Record contains only a record type id (u64) that should correspond to the IRecordType from the list of types embedded to a Wasm binary in an IT section. This is convinient for internal representations and was very convinient for prototyping at the early FCE stages.

But it has several flaws, one of the most important is that this doesn't allow to specify the exact type in host closures. So it's worth to be refactored and changed to Record(Vec<IType>).