consensus, core, ethstats: use engine specific block beneficiary (#14318)

* consensus, core, ethstats: use engine specific block beneficiary

* core, eth, les, miner: use explicit beneficiary during mining

core/headerchain.go

@@ -442,6 +442,9 @@ func (hc *HeaderChain) SetGenesis(head *types.Header) {
 // Config retrieves the header chain's chain configuration.
 func (hc *HeaderChain) Config() *params.ChainConfig { return hc.config }
 
+// Engine retrieves the header chain's consensus engine.
+func (hc *HeaderChain) Engine() consensus.Engine { return hc.engine }
+
 // GetBlock implements consensus.ChainReader, and returns nil for every input as
 // a header chain does not have blocks available for retrieval.
 func (hc *HeaderChain) GetBlock(hash common.Hash, number uint64) *types.Block {