Feature/focus (#340)

* Added and implemented Focus and FocusBySelector methods

* Added e2e tests

* Updated CHANGELOG

* Fixed linting errors

pkg/stdlib/html/focus.go

@@ -0,0 +1,38 @@
+package html
+
+import (
+	"context"
+	"github.com/MontFerret/ferret/pkg/drivers"
+	"github.com/MontFerret/ferret/pkg/runtime/core"
+	"github.com/MontFerret/ferret/pkg/runtime/values"
+)
+
+// FOCUS Calls focus on the element.
+// @param target (HTMLPage | HTMLDocument | HTMLElement) - Target node.
+// @param selector (String, optional) - Optional CSS selector. Required when target is HTMLPage or HTMLDocument.
+func Focus(ctx context.Context, args ...core.Value) (core.Value, error) {
+	err := core.ValidateArgs(args, 1, 2)
+
+	if err != nil {
+		return values.None, err
+	}
+
+	// Document with selector
+	if len(args) == 2 {
+		doc, err := drivers.ToDocument(args[0])
+
+		if err != nil {
+			return values.None, err
+		}
+
+		return values.None, doc.FocusBySelector(ctx, values.ToString(args[1]))
+	}
+
+	el, err := drivers.ToElement(args[0])
+
+	if err != nil {
+		return values.None, err
+	}
+
+	return values.None, el.Focus(ctx)
+}