cmd/geth: implement dev mode for post-merge (#27327)

This change adds back the 'geth --dev' mode of operation, using a cl-mocker. 

---------

Co-authored-by: Martin Holst Swende <martin@swende.se>
Co-authored-by: rjl493456442 <garyrong0905@gmail.com>
Co-authored-by: lightclient <14004106+lightclient@users.noreply.github.com>

internal/web3ext/web3ext.go

@@ -30,6 +30,7 @@ var Modules = map[string]string{
 	"txpool":   TxpoolJs,
 	"les":      LESJs,
 	"vflux":    VfluxJs,
+	"dev":      DevJs,
 }
 
 const CliqueJs = `
@@ -886,3 +887,22 @@ web3._extend({
 	]
 });
 `
+
+const DevJs = `
+web3._extend({
+	property: 'dev',
+	methods:
+	[
+		new web3._extend.Method({
+			name: 'addWithdrawal',
+			call: 'dev_addWithdrawal',
+			params: 1
+		}),
+		new web3._extend.Method({
+			name: 'setFeeRecipient',
+			call: 'dev_setFeeRecipient',
+			params: 1
+		}),
+	],
+});
+`