fix(checker): retry on process crash

[nicojs]

Retry checker processes when they crash unexpectedly.

• Add decorator pattern to checkers (like with test runners)
• Split "resource" related shared code in its own class
• Implement the CheckerRetryDecorator
• Add integration tests to validate that the behavior works correctly.

Fixes #3005

[nicojs]

I've tested it locally (using kill [pid]) and it works beautifully 😍

12:43:07 (1000) WARN CheckerRetryDecorator Checker process [1295] crashed with exit code null. Retrying in a new process. ChildProcessCrashedError: Child process [pid 1295] exited unexpectedly with exit code null (SIGTERM). Stdout and stderr were empty.
    at ChildProcessProxy.handleUnexpectedExit (/home/nicojs/github/stryker-js/packages/core/dist/src/child-proxy/child-process-proxy.js:34:37)
    at ChildProcess.emit (events.js:400:28)
    at maybeClose (internal/child_process.js:1055:16)
    at Process.ChildProcess._handle.onexit (internal/child_process.js:288:5) {
  innerError: undefined,
  pid: 1295,
  exitCode: null,
  signal: 'SIGTERM'
}
Mutation testing  [] 44% (elapsed: ~2m, remaining: ~2m) 97/220 tested