ethclient/simulated: implement new sim backend (#28202)

This is a rewrite of the 'simulated backend', an implementation of the ethclient interfaces
which is backed by a simulated blockchain. It was getting annoying to maintain the old
version of the simulated backend feature because there was a lot of code duplication with
the main client. 

The new version is built using parts that we already have: an in-memory geth node instance
running in developer mode provides the chain, while the Go API is provided by ethclient.
A backwards-compatibility wrapper is provided, but the simulated backend has also moved to
a more sensible import path: github.com/ethereum/go-ethereum/ethclient/simulated

---------

Co-authored-by: Felix Lange <fjl@twurst.com>
Co-authored-by: Gary Rong <garyrong0905@gmail.com>

interfaces.go

@@ -199,6 +199,16 @@ type GasPricer interface {
 	SuggestGasPrice(ctx context.Context) (*big.Int, error)
 }
 
+// GasPricer1559 provides access to the EIP-1559 gas price oracle.
+type GasPricer1559 interface {
+	SuggestGasTipCap(ctx context.Context) (*big.Int, error)
+}
+
+// FeeHistoryReader provides access to the fee history oracle.
+type FeeHistoryReader interface {
+	FeeHistory(ctx context.Context, blockCount uint64, lastBlock *big.Int, rewardPercentiles []float64) (*FeeHistory, error)
+}
+
 // FeeHistory provides recent fee market data that consumers can use to determine
 // a reasonable maxPriorityFeePerGas value.
 type FeeHistory struct {
@@ -239,3 +249,13 @@ type GasEstimator interface {
 type PendingStateEventer interface {
 	SubscribePendingTransactions(ctx context.Context, ch chan<- *types.Transaction) (Subscription, error)
 }
+
+// BlockNumberReader provides access to the current block number.
+type BlockNumberReader interface {
+	BlockNumber(ctx context.Context) (uint64, error)
+}
+
+// ChainIDReader provides access to the chain ID.
+type ChainIDReader interface {
+	ChainID(ctx context.Context) (*big.Int, error)
+}