CC Mode: introduce a new cache for brace structures. This fixes bug #45248

CC Mode: introduce a new cache for brace structures.  This fixes bug #45248

Also fix three infinite loops.  The new cache accelerates backward searches
for struct beginnings in c-looking-at-or-maybe-in-bracelist.

* lisp/progmodes/cc-engine.el (c-beginning-of-statement-1): In the final loop
over unary operators, add a check (> (point) lim) to avoid certain infinite
loops.
(c-beginning-of-decl-1): In the first loop add a similar check on point and
lim.
(c-laomib-loop): New function extracted from
c-looking-at-or-maybe-in-bracelist.
(c-laomib-cache): New buffer local variable.
(c-laomib-get-cache, c-laomib-put-cache, c-laomib-fix-elt)
(c-laomib-invalidate-cache): New functions which implement the cache.
(c-looking-at-or-maybe-in-bracelist): Replace two invocations of
c-go-up-list-backwards with calls to c-parse-state.  Extract the new function
c-laomib-loop.  Insert code which calls c-laomib-loop minimally, with the help
of the new cache.

* lisp/progmodes/cc-mode.el (c-basic-common-init): Initialise the new cach
(at mode start).
(c-before-change): Invalidate the new cache.
(c-fl-decl-start): Add an extra check (> (point) bod-lim) to prevent looping.
Determine the enclosing brace to pass as arguments to
c-looking-at-or-maybe-in-bracelist.