An optimized string type for unique names. [StringName]s are immutable strings designed for general-purpose representation of unique names. [StringName] ensures that only one instance of a given name exists (so two [StringName]s with the same value are the same object). Comparing them is much faster than with regular [String]s, because only the pointers are compared, not the whole strings. Constructs an empty [StringName]. Constructs a [StringName] as a copy of the given [StringName]. Creates a new [StringName] from the given [String].