Add {fork_name}_enabled functions (#5951)

* add fork_name_enabled fn to Forkname impl

* refactor codebase to use new fork_enabled fn

* fmt

* Merge branch 'unstable' of https://github.com/sigp/lighthouse into fork-ord-impl

* small code cleanup

* resolve merge conflicts

* fix beacon chain test

* merge conflicts

* fix ef test issue

* resolve merge conflicts

beacon_node/execution_layer/src/test_utils/mock_builder.rs

@@ -479,16 +479,18 @@ pub fn serve<E: EthSpec>(
                 let prev_randao = head_state
                     .get_randao_mix(head_state.current_epoch())
                     .map_err(|_| reject("couldn't get prev randao"))?;
-                let expected_withdrawals = match fork {
-                    ForkName::Base | ForkName::Altair | ForkName::Bellatrix => None,
-                    ForkName::Capella | ForkName::Deneb | ForkName::Electra => Some(
+
+                let expected_withdrawals = if fork.capella_enabled() {
+                    Some(
                         builder
                             .beacon_client
                             .get_expected_withdrawals(&StateId::Head)
                             .await
                             .unwrap()
                             .data,
-                    ),
+                    )
+                } else {
+                    None
                 };
 
                 let payload_attributes = match fork {