State: StateValidator should verify that content belongs to the canonical chain

[morph-dev]

At the moment, our StateValidator doesn't verify that content value is part of the canonical chain.

The StateContentValue contains the block_hash that we should use to fetch block header. We should also verify that received header is part of the canonical chain.

From header we can get the state_root which is enough to use with the trie proof (which is already implemented).