Use timer accessors instead of aref/aset

Use timer accessors instead of aref/aset

* lisp/emacs-lisp/timer-list.el (list-timers):
* lisp/gnus/mail-source.el (mail-source-start-idle-timer):
* lisp/play/gamegrid.el (gamegrid-set-timer):
* lisp/progmodes/vhdl-mode.el (vhdl-run-when-idle):
* lisp/simple.el (analyze-text-conversion):
* lisp/time.el (display-time-event-handler):
Use timer accessors.

(cherry picked from commit e56e4b345a25194bc7adb83523e8d886b718c9fa)