FileSystemAccessServer: Add service for accessing veiled files nicely

Adds new service FileSystemAccessServer which allows programs to
request a file descriptor for any file on the file system.

The user can be prompted to choose the path with a FilePicker, or the
path can be provided by the application which will show a MessageBox
showing the pid and name of the calling process and allows the user to
approve or deny the request.

Userland/Services/FileSystemAccessServer/FileSystemAccessClient.ipc

@@ -0,0 +1,3 @@
+endpoint FileSystemAccessClient
+{
+}