Browser+LibWeb+WebContent: Allow Browser to load local files

To achieve this goal:
 - The Browser unveils "/tmp/portal/filesystemaccess"
 - Pass the page through LoadRequest => ResourceLoader
 - ResourceLoader requests a file to the FileSystemAccessServer via IPC
 - OutOfProcessWebView handles it and sends a file descriptor back to
 the Page.

Userland/Libraries/LibWeb/CMakeLists.txt

@@ -274,6 +274,7 @@ set(SOURCES
     Layout/TextNode.cpp
     Layout/TreeBuilder.cpp
     Loader/ContentFilter.cpp
+    Loader/FileRequest.cpp
     Loader/FrameLoader.cpp
     Loader/ImageLoader.cpp
     Loader/ImageResource.cpp