Fix MSVC C2365: replace TokenType alias with non-conflicting TT

MSVC (Windows SDK 10.0.26100.0) refuses to shadow the enumerator
TOKEN_INFORMATION_CLASS::TokenType from winnt.h with a using type
alias, reporting C2365 redefinition. All 4 C++ test files now use
  using TT = midigpt::TokenType;
and TT:: for all enum value accesses, which avoids the collision.

Author: DaoTwenty