LS: include tokens in tree during parsing 

Currently parser drops lots of token information on the floor which is fine for batch compilation. However language service still needs this data so to reconstruct it we now re-scan the source text. This PR contains proposal for implementation strategy to augment the parser with a few extensibility points so LS can plug in into the parsing process and embed token information into the tree during parsing.
Why not use no op function by default and set it to different function when calling from LS. that way there is no extra checks and the inline functions can be optimized during normal tsc runs?