The source location of this Dart language entity, or null if the
entity is synthetic.
If the reflectee is a variable, the returned location gives the position of the variable name at its point of declaration.
If the reflectee is a library, class, typedef, function or type variable with associated metadata, the returned location gives the position of the first metadata declaration associated with the reflectee.
Otherwise:
If the reflectee is a library, the returned location gives the position of the keyword 'library' at the reflectee's point of declaration, if the reflectee is a named library, or the first character of the first line in the compilation unit defining the reflectee if the reflectee is anonymous.
If the reflectee is an abstract class, the returned location gives the position of the keyword 'abstract' at the reflectee's point of declaration. Otherwise, if the reflectee is a class, the returned location gives the position of the keyword 'class' at the reflectee's point of declaration.
If the reflectee is a typedef the returned location gives the position of the of the keyword 'typedef' at the reflectee's point of declaration.
If the reflectee is a function with a declared return type, the returned location gives the position of the function's return type at the reflectee's point of declaration. Otherwise. the returned location gives the position of the function's name at the reflectee's point of declaration.
This operation is optional and may throw an UnsupportedError.