Experiment - monomorphic node/type/signature

[dragomirtitian]

Experiment to make several objects monomorphic by keeping the common properties in a single object shape and moving all other properties to a separate object and using accessors to preserve compatibility with existing code.

Local improvements seem promising, building TSC/compiler: ~-20% in time with ~+10% in memory.

Code is rough around the edges, just testing out as a proof of concept.

Note: This is the result of me and @acutmore bouncing ideas about improving access to Node.kind