TEnum::GetEnum("B")->GetUnderlyingType() does not following typedefs

[pcanal]

As first reported in #12685:

The problem of not resolving typdefs extends to the specification of the underlying integer type, e.g.

    enum A : int {};
    TEnum::GetEnum("A")->GetUnderlyingType()  // --> (EDataType) (kInt_t) : (int) 3

but

    enum B : std::int32_t {};
    TEnum::GetEnum("B")->GetUnderlyingType()  // --> (EDataType) (kNumDataTypes) : (int) 23