CC Mode: Fix the timing of application and removal of string fence properties

CC Mode: Fix the timing of application and removal of string fence properties

This fixes bug #36897.

* lisp/progmodes/cc-mode.el (c-before-change-check-unbalanced-strings): Check
string fence text properties are actually present on string delimiters before
trying to remove them.
(c-before-change): Amend the nesting of unwind-protect, widen,
c-restore-string-fences, and c-clear-string-fences.  Move
invalidate-state-cache to outside of the widening.
(c-after-change): Amend the nesting of unwind-protect, widen,
c-restore-string-fences, and c-clear-string-fences.