Use fork instead of spawn for AppWorker

[itoys]

Fixes #758

[itoys]

When we use spawn and send message from subprocess with process.send({workerLoaded:true}) we get following error:

SyntaxError: Unexpected token L in JSON at position 0
    at JSON.parse (<anonymous>)
    at Pipe.channel.onread (internal/child_process.js:471:28)

While debugging JSON.parse I saw that it got following message Loaded:true})
I believe that this issue related to nodejs/node#21671
Because of when we use spawn from file running in electron, spawn use system node, instead of fork which use node from electron

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@46e2461). Click here to learn what that means.
The diff coverage is 66.66%.

@@            Coverage Diff            @@
##             master     #760   +/-   ##
=========================================
  Coverage          ?   14.39%           
=========================================
  Files             ?       63           
  Lines             ?     3259           
  Branches          ?      416           
=========================================
  Hits              ?      469           
  Misses            ?     2790           
  Partials          ?        0

Impacted Files	Coverage Δ
src/debugger/nodeDebugWrapper.ts	2.91% <0%> (ø)
src/debugger/forkedAppWorker.ts	86.56% <100%> (ø)