add code generation phase to Compilation
add `output.iife` options to remove iife wrapper
add `experiments.outputModule` which enabled `output.module`
add `output.module` which sets defaults to `output.iife: false`, `output.libraryTarget: "module"`, `output.jsonpScriptType: "module"`, `terserOptions.module: true`
add `output.module` example
improve runtime requirements needed by ConcatenatedModule
add entry inlining, which inlines entry module code into runtime scope (only when safe)
make whole bundle strict when all modules are strict
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`