TASTy as a Standard for Scala

[bishabosha]

This is a meta issue to collect issues regarding TASTy becoming a standard reference for the semantics of Scala, and removal of dotc implementation details from its binary representation.

• compiler internal types/symbols appearing in TASTy
  • scala.& and scala.| Dotty pickles type trees of | and & to applied type tree of fictional symbols #7688 - yes they are legitimate types
  • method java.lang.Enum.<init>: ()java.lang.Enum extending java.lang.Enum should be desugared before TASTy  #7478
  • annotation encoding bounds of an Opaque type alias Generalize TypeBoundsTree to bounded opaque aliases #8212
  • scala.annotation.internal.Child To enumerate exhaustivity of sealed types
  • Special UTF8 names that should be escaped from symbolic encoding (and therefore clash with any backtick escaped names):
    • <init>, <empty>, "", <repeated>, []
  • default method parameters are encoded as definitions [Issue required]
  • empty synthetic companion object for value classes [Issue required]
• more efficient enumeration of parents TASTy should list the types of template parents #8028
• dotc independent sub-typing implementation
• TASTy interpreter