Guess the file that defined the Lisp object OBJECT, of type TYPE.
OBJECT should be a symbol associated with a function, variable, or face;
alternatively, it can be a function definition.
If TYPE is `defvar', search for a variable definition.
If TYPE is `defface', search for a face definition.
If TYPE is the value returned by `symbol-function' for a function symbol,
search for a function definition.
The return value is the absolute name of a readable file where OBJECT is
defined. If several such files exist, preference is given to a file
found via `load-path'. The return value can also be `C-source', which
means that OBJECT is a function or variable defined in C. If no
suitable file is found, return nil. (fn OBJECT TYPE)