core: allow external code to set the block validator for malicious tests (#25119)

* core: don't validate state

* core: allow external validator

* core: revert

* core: comments

* Update blockchain_reader.go

* core: move SetValidator to blockchain.go

* core: rename method

core/blockchain.go

@@ -2374,3 +2374,10 @@ func (bc *BlockChain) InsertHeaderChain(chain []*types.Header, checkFreq int) (i
 	_, err := bc.hc.InsertHeaderChain(chain, start, bc.forker)
 	return 0, err
 }
+
+// SetBlockValidatorForTesting sets the current validator.
+// This method can be used to force an invalid blockchain to be verified for tests.
+// This method is unsafe and should only be used before block import starts.
+func (bc *BlockChain) SetBlockValidatorForTesting(v Validator) {
+	bc.validator = v
+}