Use Block Interface Across Prysm (#8918)

* commit initial work

* checkpoint current work

* gaz

* checkpoint

* req/resp changes

* initial-sync

* finally works

* fix error

* fix bugs

* fix issue

* fix issues

* fix refs

* tests

* more text fixes

* more text fixes

* more text fixes

* fix tests

* fix tests

* tests

* finally fix builds

* finally

* comments

* fix fuzz

* share common library

* fix

* fix

* add in more defensive nil checks

* add in more defensive nil checks

* imports

* Apply suggestions from code review

Co-authored-by: terence tsao <terence@prysmaticlabs.com>

* Apply suggestions from code review

Co-authored-by: terence tsao <terence@prysmaticlabs.com>

* Update shared/interfaces/block_interface.go

Co-authored-by: terence tsao <terence@prysmaticlabs.com>

* Update shared/interfaces/block_wrapper.go

Co-authored-by: terence tsao <terence@prysmaticlabs.com>

* Update shared/interfaces/block_interface.go

Co-authored-by: terence tsao <terence@prysmaticlabs.com>

* imports

* fix bad changes

* fix

* terence's review

* terence's review

* fmt

* Update beacon-chain/rpc/beacon/blocks.go

Co-authored-by: Radosław Kapka <rkapka@wp.pl>

* fix tests

* fix

* fix all tests

Co-authored-by: terence tsao <terence@prysmaticlabs.com>
Co-authored-by: Radosław Kapka <rkapka@wp.pl>

beacon-chain/sync/initial-sync/service.go

@@ -140,7 +140,7 @@ func (s *Service) Initialized() bool {
 // behind the current network head.
 func (s *Service) Resync() error {
 	headState, err := s.cfg.Chain.HeadState(s.ctx)
-	if err != nil || headState == nil {
+	if err != nil || headState == nil || headState.IsNil() {
 		return errors.Errorf("could not retrieve head state: %v", err)
 	}