class SyntaxTree::LBracket

provides a default node.
easier to create LBracket nodes without any specific value, this method
another node. This means it's required at initialization time. To make it
to it if they occur in the source, oftentimes an LBracket is a child of
Because some nodes keep around a [ token so that comments can be attached

def self.default
  new(value: "[", location: Location.default)
end