core,eth: call frame tracing (#23087)

This change introduces 2 new optional methods; `enter()` and `exit()` for js tracers, and makes `step()` optiona. The two new methods are invoked when entering and exiting a call frame (but not invoked for the outermost scope, which has it's own methods). Currently these are the data fields passed to each of them:

    enter: type (opcode), from, to, input, gas, value
    exit: output, gasUsed, error

The PR also comes with a re-write of the callTracer. As a backup we keep the previous tracing script under the name `callTracerLegacy`. Behaviour of both tracers are equivalent for the most part, although there are some small differences (improvements), where the new tracer is more correct / has more information.

eth/tracers/tracer_test.go

@@ -236,3 +236,35 @@ func TestIsPrecompile(t *testing.T) {
 		t.Errorf("Tracer should consider blake2f as precompile in istanbul")
 	}
 }
+
+func TestEnterExit(t *testing.T) {
+	// test that either both or none of enter() and exit() are defined
+	if _, err := New("{step: function() {}, fault: function() {}, result: function() { return null; }, enter: function() {}}", new(Context)); err == nil {
+		t.Fatal("tracer creation should've failed without exit() definition")
+	}
+	if _, err := New("{step: function() {}, fault: function() {}, result: function() { return null; }, enter: function() {}, exit: function() {}}", new(Context)); err != nil {
+		t.Fatal(err)
+	}
+
+	// test that the enter and exit method are correctly invoked and the values passed
+	tracer, err := New("{enters: 0, exits: 0, enterGas: 0, gasUsed: 0, step: function() {}, fault: function() {}, result: function() { return {enters: this.enters, exits: this.exits, enterGas: this.enterGas, gasUsed: this.gasUsed} }, enter: function(frame) { this.enters++; this.enterGas = frame.getGas(); }, exit: function(res) { this.exits++; this.gasUsed = res.getGasUsed(); }}", new(Context))
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	scope := &vm.ScopeContext{
+		Contract: vm.NewContract(&account{}, &account{}, big.NewInt(0), 0),
+	}
+
+	tracer.CaptureEnter(vm.CALL, scope.Contract.Caller(), scope.Contract.Address(), []byte{}, 1000, new(big.Int))
+	tracer.CaptureExit([]byte{}, 400, nil)
+
+	have, err := tracer.GetResult()
+	if err != nil {
+		t.Fatal(err)
+	}
+	want := `{"enters":1,"exits":1,"enterGas":1000,"gasUsed":400}`
+	if string(have) != want {
+		t.Errorf("Number of invocations of enter() and exit() is wrong. Have %s, want %s\n", have, want)
+	}
+}