[core] Allow any action if action creators are not specified in model

[davidkpiano]

This PR fixes a regression noticed by some users - when they specified events but not actions in createModel(...), actions would be typed as never:

    const model = createModel(
      {},
      {
        events: {}
      }
    );

    model.createMachine({
      // TS will not compile
      entry: 'someAction',
      exit: { type: 'someObjectAction' },
    });

Fixes #2619

[changeset-bot]

🦋 Changeset detected

Latest commit: f8cf5df

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
xstate	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[Andarist]

This change has completely broken the inference of actions:

const model = createModel({ foo: 100 }, {
  events: {
    BAR: () => ({})
  }
})

model.createMachine({
  // ctx is being any
  entry: (ctx) => {},
  exit: assign({
    // ctx is being unknown
    foo: (ctx) => 42
  })
})