LibWebView: Define the list of built-in search engines in LibWebView

These engines and their query URLs are duplicated in several places.
Before implementing search support in the AppKit chrome, let's move
these engines to LibWebView.

Userland/Libraries/LibWebView/CMakeLists.txt

@@ -9,6 +9,7 @@ set(SOURCES
     DOMTreeModel.cpp
     History.cpp
     RequestServerAdapter.cpp
+    SearchEngine.cpp
     SourceHighlighter.cpp
     StylePropertiesModel.cpp
     URL.cpp