Added new test VF font (a subset of NotoSans-VF only containing glyphs 'A', 'Agrave' and 'T');
the VF was instanced with varLib.mutator, producing a series of full instances, which are
included as ttx files as well.
The tests run the partial instancer twice, once only instancing wght, then again for wdth,
and assert that the generated instance is identical to those.
6efc66e0fc