Allow 'make-cursor-line-fully-visible' name a function

Allow 'make-cursor-line-fully-visible' name a function

* src/xdisp.c (cursor_row_fully_visible_p): Handle the case of
make-cursor-line-fully-visible being a function.  Accept a 3rd
argument; if non-zero, assume the caller already tested the
conditions for the cursor being fully-visible, and don't
recheck them.  All callers changed.
(try_cursor_movement, try_window_id): Call
cursor_row_fully_visible_p instead of testing the value of
make-cursor-line-fully-visible directly.
(syms_of_xdisp) <make-cursor-line-fully-visible>: Update the
doc string.  Define a symbol Qmake_cursor_line_fully_visible.
(Bug#32848)

* lisp/cus-start.el (standard): Update the Custom form.

* etc/NEWS: Mention the change in possible values of
'make-cursor-line-fully-visible'.