Move progressive-list root helper functions to chainsafe/ssz

Recent chainsafe/lodestar#9390 contains some utility functions that should be moved to ssz library.

See https://github.com/ChainSafe/lodestar/blob/17a48050e67af1c339b28f1283d5c2f04dc60bc1/packages/state-transition/src/util/ssz.ts#L4

Start with the linked Lodestar file packages/state-transition/src/util/ssz.ts at line 4 and identify the progressive-list root helper functions referenced by the issue. Inspect the ssz package structure and existing tests to determine their destination and expected behavior. Done means the helpers live in the ssz library and Lodestar can use them from there without retaining the duplicated utility code.

Written by the indexing model from the issue text.