Add a `trie_root_hash` variant for chain specs genesis (#10140)

* Add a `hash` variant for chain specs

* Add doc

* Rename to TrieRootHash

* Apply suggestions from code review

Co-authored-by: Bastian Köcher <[email protected]>

* Rustfmt

* More cargo fmt I guess

* Ok I have to use nightly cargo fmt

Co-authored-by: Bastian Köcher <[email protected]>