process: refactor bootstrap of worker/main thread stdio, fatalException, and script evaluation

[joyeecheung]

process: move eval and exception bootstrap ito process/execution.js

This patch:

• Moves tryGetCwd, evalScript and fatalException from
  bootstrap/node.js into process/execution.js so that
  they do have to be passed into the worker thread
  setup function, instead the worker code can require them
  when necessary.
• Moves setUncaughtExceptionCaptureCallback and
  hasUncaughtExceptionCaptureCallback along with the two
  global state exceptionHandlerState and
  shouldAbortOnUncaughtToggle info process.execution.js
  as those are only used by the fatalException and these
  two accessors as one self-contained unit.

process: split worker IO into internal/worker/io.js

• Move setupProcessStdio which contains write access to
  the process object into bootstrap/node.js
• Move MessagePort, MessageChannel, ReadableWorkerStdio,
  and WritableWorkerStdio into internal/worker/io.js
• Move more worker-specific bootstrap code into
  internal/process/worker_thread_only from setupChild
  in internal/worker.js, and move the process._fatalException
  overwrite into bootstrap/node.js for clarity.

process: move worker bootstrap code into worker_thread_only.js

Move worker bootstrap code into worker_thread_only.js from
internal/worker.js since they are only run once during bootstrap.

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• commit message follows commit guidelines