Add current iteration's browser getter method to VU

Add a higher level helper method to VU in order to retrieve the current
VU iteration's browser instance. This improves the repetitive calls to
getBrowser() method passing the current iteration as input from the
mapping layer.

browser/mapping.go

@@ -676,21 +676,21 @@ func mapBrowser(vu moduleVU) mapping {
 	rt := vu.Runtime()
 	return mapping{
 		"contexts": func() ([]api.BrowserContext, error) {
-			b, err := vu.getBrowser(vu.State().Iteration)
+			b, err := vu.browser()
 			if err != nil {
 				return nil, err
 			}
 			return b.Contexts(), nil
 		},
 		"isConnected": func() (bool, error) {
-			b, err := vu.getBrowser(vu.State().Iteration)
+			b, err := vu.browser()
 			if err != nil {
 				return false, err
 			}
 			return b.IsConnected(), nil
 		},
 		"newContext": func(opts goja.Value) (*goja.Object, error) {
-			b, err := vu.getBrowser(vu.State().Iteration)
+			b, err := vu.browser()
 			if err != nil {
 				return nil, err
 			}
@@ -702,21 +702,21 @@ func mapBrowser(vu moduleVU) mapping {
 			return rt.ToValue(m).ToObject(rt), nil
 		},
 		"userAgent": func() (string, error) {
-			b, err := vu.getBrowser(vu.State().Iteration)
+			b, err := vu.browser()
 			if err != nil {
 				return "", err
 			}
 			return b.UserAgent(), nil
 		},
 		"version": func() (string, error) {
-			b, err := vu.getBrowser(vu.State().Iteration)
+			b, err := vu.browser()
 			if err != nil {
 				return "", err
 			}
 			return b.Version(), nil
 		},
 		"newPage": func(opts goja.Value) (mapping, error) {
-			b, err := vu.getBrowser(vu.State().Iteration)
+			b, err := vu.browser()
 			if err != nil {
 				return nil, err
 			}

browser/modulevu.go

@@ -3,6 +3,7 @@ package browser
 import (
 	"context"
 
+	"github.com/grafana/xk6-browser/api"
 	"github.com/grafana/xk6-browser/k6ext"
 
 	k6modules "go.k6.io/k6/js/modules"
@@ -19,6 +20,11 @@ type moduleVU struct {
 	*browserRegistry
 }
 
+// browser returns the VU browser instance for the current iteration.
+func (vu moduleVU) browser() (api.Browser, error) {
+	return vu.browserRegistry.getBrowser(vu.State().Iteration)
+}
+
 func (vu moduleVU) Context() context.Context {
 	// promises and inner objects need the VU object to be
 	// able to use k6-core specific functionality.