This is the first in a sequence of changes that change the block:: items
to not include Block as a prefix in their name, in accordance with the
Rust API guidelines.
It's not accurate to call it a LightClientRootHash, because it's not
always a root has for a light client -- sometimes it's a different kind
of root hash.
This moves the tests::generate module into the block tests. Because
this whole set of changes is just focused on reorganization, the
generate code is unchanged, but in the future, the code should be
rewritten as a collection of proptest strategies.
Henry de Valence