Custom glob patterns tie the implementation (Using Dir.glob) to the API
we provide.

It also doesn't really work. extract_handler_and_format_and_variant
expects the handler, format, and variant to be at the end of the
template path, and in the same order as they are in the default pattern.

This deprecates specifying a custom path for FileSystemResolver and
removes the pattern argument of OptimizedFileSystemResolver#initialize,
which does not work with a custom pattern.