tech(fmt/psl): prep-work for further language-server support (#4933)
add documentation helper to Top
add name helper to FieldType
Added more positions:
ModelPosition::Name
FieldPosition::{Name,Type}
SourcePosition::Name
GeneratorPosition
CompositeTypePosition
split out find_at_position
added find_at_position doc
Added topwalker
some clean-up of publicity
added indexing for generatorid on schema ast