Like `get-char-property', but with extra overlay information.
The value is a cons cell. Its car is the return value of `get-char-property'
with the same arguments--that is, the value of POSITION's property
PROP in OBJECT. Its cdr is the overlay in which the property was
found, or nil, if it was found as a text property or not found at all.
OBJECT is optional and defaults to the current buffer. OBJECT may be
a string, a buffer or a window. For strings, the cdr of the return
value is always nil, since strings do not have overlays. If OBJECT is
a window, then that window's buffer is used, but window-specific
overlays are considered only if they are associated with OBJECT. If
POSITION is at the end of OBJECT, both car and cdr are nil. (fn POSITION PROP &optional OBJECT)