feat(Variant): add FromValue/ToValue helpers

[poirierlouis]

Changes

• convert a Variant to/from a value. Support fundamental and common types.
• add constness on Extract method, implementation is already readonly.

Usages
Static:

RED4ext::Variant data;
RED4ext::Variant::FromValue<uint64_t>(42, data); // return false on error

uint64_t hash;
RED4ext::Variant::ToValue(data, hash); // return false on error

Static without direct error feedback:

RED4ext::Variant data = RED4ext::Variant::FromValue<uint64_t>(42);
const auto hash = RED4ext::Variant::ToValue<uint64_t>(data);

Set/Get directly on an instance:

RED4ext::Variant data;
data.Set<uint64_t>(42); // return false on error

const auto hash = data.Get<uint64_t>();

Notes
This is a first step. In the end, integrating implementation from RedLib would likely be the best solution for end-users. I left a comment about this.

[poirierlouis]

I'll take a look at Resolving from RedLib, and write a dedicated PR.

[wopss]

Thanks!

[poirierlouis]

I'll update CHANGELOG and I guess it will be ready to merge?

[wopss]

Yes.