Merkle Mountain Range pallet improvements (#7891)

* Add stateless verification helper function.

* Split MMR primitives.

* Add RuntimeAPI

* RuntimeAPI with OpaqueLeaves

* Bump spec_version,.

* Move primitives back to frame.

* Fix OpaqueLeaf encoding.

* Add block number to frame_system implementation of LeafDataProvider.

* Relax leaf codec requirements and fix OpaqueLeaf

* Add root to debug line.

* Apply suggestions from code review

Co-authored-by: Hernando Castano <[email protected]>

* Typo.

Co-authored-by: Hernando Castano <[email protected]>