Bring the gap and minimize the static compile if else LIGHT_EXPREESSION in the TryEmit methods

[dadhi]

Make TryClosureInfoCollect/EmittingVisitor writeable struct instead static class.
Keep the current public surface CompileFast API which internally will create FEC struct.
Move TryCollect snd TryEmit parameters into the FEC fields e'cept for current Expression and ParentFlags and byRefIndex as parameters.
Unpack ClosureInfo fields directly into FEC struct.
Avoid FEC stuct copy as it is quite fat.