Returns the enum constant of this class with the specified name.
The string must match exactly an identifier used to declare an
enum constant in this class. (Extraneous whitespace characters are
not permitted.)
Parameters:
name - the name of the enum constant to be returned.
TextDirection for a valid label ('ltr or 'rtl').
This function returns null for an invalid label.
The calling code is expected to give a context-sensitive error message if null is returned.