Support new tags in TASTy 28.5

[bishabosha]

• [ ] TRACKED (flag)
• [ ] FLEXIBLEtype (type)
• [ ] QUOTE (tree)
• [ ] SPLICE (tree)
• [ ] QUOTEPATTERN (tree)
• [ ] SPLICEPATTERN (tree)

[sjrd]

TRACKED is behind an experimental feature gate and is not part of the standard, so this is not one tasty-query will support at this time.

FLEXIBLEtype is part of the gray area of explicit nulls, which are not TASTy-experimental, so we'll "support" it by being able to read it, but we don't yet provide any real guarantee about explicit-null codebases.