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.