[core] Add mapStates(…)

[davidkpiano]

Add mapState(snapshot, mapper) to map a snapshot to values based on active state(s).

import { mapState } from 'xstate';

const results = mapState(snapshot, {
  states: {
    loading: { map: () => 'Loading...' },
    success: { map: (snap) => snap.context.data },
    error: { map: (snap) => snap.context.error.message }
  }
});

console.log(results);
// E.g. if snapshot.value === 'loading', then:
// [
//   { stateNode: { key: 'loading' }, result: 'Loading...' }
// ]

[changeset-bot]

🦋 Changeset detected

Latest commit: d220665

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

This PR includes changesets to release 5 packages

Name	Type
xstate	Minor
@xstate/react	Major
@xstate/solid	Major
@xstate/svelte	Major
@xstate/vue	Major

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