this just implements the requester side of things, and does not work
because there is no support in the state dumper for this. But it sets up
all the logic to request state headers and parts in the new way

…her than catching up for chunk production

This makes it simpler overall. Also refactor this function to return
an enum saying what to do instead of two bools, which was a little
bit confusing before.

…t_epoch_start_sync_hash()

…t_sync_hash()

make this just one get_sync_hash() with the protocol feature logic in there, and
make the other two private

this was moved to the Client so we could call it in tests in 9ae019a
but now that we have a Chain::get_sync_hash() function, this is no longer needed

previous epoch -> V0
current epoch -> V1

more clear what is being talked about

This test fails because the mock epoch manager does not implement
get_block_info(), which is needed in the new implementation of get_sync_hash().
Instead of trying to fix it, just move the test to test loop

Otherwise this might return an error when looking up the prev header
in get_current_epoch_sync_hash(), and we don't want to sync state from
before the genesis anyway

…ync_hash_validity()

The behavior has changed to return false for the genesis block, but getting the sync hash corresponding
to the genesis block is not something we ever want to do, since we're not going to be syncing that state,
and there's an assertion that checks we dont use the genesis hash as a sync hash in ClientActorInner::find_sync_hash()
anyway.

…revious epoch)

The node will actually dump state in the first epoch now with current
epoch state sync