bug#22692: docstring for xref-find-definitions

[Mike Kupfer]

Based on the behavior that I observe (using "emacs -Q" to visit
src/frame.c), the docstring for xref-find-definitions would be more
accurate if the first paragraph were replaced by

  Find the definition of the identifier at point.
  If there is no identifier at point, use an identifier (or numeric
  literal) near point on the same line.  With a prefix argument or when
  there’s no identifier on the current line, prompt for the identifier
  to look up.

Trying to look up the definition for a numeric literal strikes me as
odd, but that's the behavior I'm seeing.

mike