[core] Strongly-typed meta keys

[davidkpiano]

This PR introduces:

• Internal types for computing state IDs from a state schema (the machine configuration)
• Strongly-typing snapshot.getMeta() to use those state IDs as keys

[changeset-bot[bot]]

🦋 Changeset detected

Latest commit: e79ad4e223053310e9d63e9192198cf19df7b979

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

This PR includes changesets to release 1 package

| Name | Type | | ------ | ----- | | xstate | Minor |

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