LibWeb+WebContent: Add a simple API for running arbitrary JavaScript

This patch adds OutOfProcessWebView::run_javascript(StringView).
This can be used by the OOPWV embedder to execute arbitrary JavaScript
in the top-level browsing context on the WebContent process side.

Userland/Libraries/LibWeb/OutOfProcessWebView.h

@@ -35,6 +35,8 @@ public:
     void js_console_initialize();
     void js_console_input(const String& js_source);
 
+    void run_javascript(StringView);
+
     String selected_text();
     void select_all();