Drafting a Slot API
Make StartPointBuilder use slots

o Tests :)
o Got rid of SlotAccess, seemed premature to have that abstraction
o StartItem.rewrite
Rewriting the whole query
Make IndexLookupBuilder declare slots
Make SlotIdentifier not inherit from Identifier

o Introduce helpers for rewriting expressions and query tokens
o GDSTestBase: Rename planContext to createPlanContext
In medias res