Self-contained `State` module

[imalygin]

This is the logical continuation of the Public Merkle API initiative (#10988). Also, it overlaps with #14772.

Currently, a Block node would have to not only use the swirlds-state-api module but also swirlds-platform-core as a dependency, which, in turn, contains functionality that is not relevant in the context of the state (consensus, gossip, transaction handling).

We need a State module that has not only a set of API interfaces but also all the necessary implementations to represent the full Merkle state.

### Tasks
- [ ] Rename `swirlds-state-api` to more appropriate `swirlds-state`
- [ ] Create a design doc outlining all the necceary changes required for this module