[core] Add support for handling communication errors

[davidkpiano]

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This PR adds support for handling communication errors when the targets of events sent between actors does not exist:

// ...
entry: sendParent('SOME_EVENT'), // pretend the parent does not exist...
on: {
  'error.communication': {
    actions: (_, e) => { console.log(e.message); }  // this will happen instead of an error being thrown
  }
}

If there is no 'error.communication' transition, then an error will be thrown (existing behavior).

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Latest commit: 4fc6979706b0a10fc005296bfd03f102099ca421

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[huan]

Can we have error.communication defined as an enum or literal string so that we can import and use it with static typed?

i.e.:

enum XStateTypes {
  ErrorCommnication = 'error.communication'
}

import { XStateTypes } from 'xstate/types'

// ...
entry: sendParent('SOME_EVENT'), // pretend the parent does not exist...
on: {
  [XStateTypes.ErrorCommunication]: {
    actions: (_, e) => { console.log(e.message); }  // this will happen instead of an error being thrown
  }
}

[Andarist]

Error handling might still require some work in v5 but I think that it will look different than what we have here so this PR can be closed for now.