Convert YYInitialTest to Parameterized

Push parameterization down to Test.
Parameterize SigilTest
Parameterize InterpolationTest

Had to moving closing brace test to a interpolation.EndTest because it
had unique state setup.
Parameterize GroupHeredocStartTest
Parameterize/Theorify AtomStartTest

Convert the assertWholeAtom tests to atom_start.WholeTest theory while
other tests become parameterized in atom_start.FragmentTest.
Parameterize AtomBodyTest
Parameterize named_sigil tests
Parameterize group Tests
Parameterize group_heredoc_end.quote Tests

Had to add ability to check that entire buffer is _NOT_ consumed in
TokenTest#token to cover the pushback of terminators of the wrong quote
type.
Parameterize group_heredoc_end.sigil tests
Parameterize group_heredoc_line_body Tests
Parameterize group_heredoc_line_start.quote Tests
Parameterize group_heredoc_line_start.sigil Tests