Update `RuntimeVerison` type and use `system_version` to derive extrinsics root `StateVersion` instead of `V0` (#4257)

This PR 
- Renames `RuntimeVersion::state_version` to `system_version`
- Uses `Runtime::system_version` to derive extrinsics root
`StateVersion` instead of default `StateVersion::V0`

This PR should not be breaking any existing chains so long as they use
same `RuntimeVersion::state_version` for `Runtime::system_version`

Using `RuntimeVersion::system_version = 2` will make the extrinsics root
to use `StateVersion::V1` instead of `V0`

RFC for this change - https://github.com/polkadot-fellows/RFCs/pull/42

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Co-authored-by: Bastian Köcher <git@kchr.de>
Co-authored-by: Koute <koute@users.noreply.github.com>
Co-authored-by: Nazar Mokrynskyi <nazar@mokrynskyi.com>