use variable tagging in harmony pluging (instead of magic renaming)
Parser no longer calls hooks.expression for x in `x = ...`, hooks.pattern is called instead
remove rootName argument from hooks.expressionMemberChain and hooks.callMemberChain
fix a bug with prefetching initial chunks
InitFragments have get[End]Content methods which get a sourceContext
RuntimeModules have implicit chunk and compilation
changed default to `output.ecmaVersion: 2015`