Singelton uniontypes containing non-singelton uniontypes are not treated as singeltons

[John Tinnerholm]

Singelton uniontypes containing a non singleton uniontype is not treated as a singelton:

uniontype UT
  record R
    Real RI;
  end R;
  function f
    output Real ro;
  protected
    UT tmpUT = R(1.0);
  algorithm
    ro := tmpUT.RI;
  end f;
  uniontype UT2
    record R1
    end R1;
    record R2
    end R2;
  end UT2;
end UT;

This is typically not an issue, but it occurs in the new frontend where uniontypes are used at the top level and contains non-singeltons within them.

Trying to access the component R at the top level currently results in

Error: Internal error Types.getMetaRecordFields called on a non-singleton uniontype: UT

[John Tinnerholm]

Adjusted in:

​https://github.com/OpenModelica/OpenModelica/commit/6d60ea0b5dcbca8a32be98e5e5400b3ec0b9de32