Correctly fontify C++ direct initializations with parens inside functions

Correctly fontify C++ direct initializations with parens inside functions

Or, more clearly, when something looks like a function declaration and it's
inside a function, fontify it as a direct initialization.

For this purpose, introduce a "brace stack" for each buffer, where an entry on
the brace stack states how deeply nested a particular position is inside
braces inside a "top level", which includes classes and namespaces.

Also introduce a new "context", "top", with which c-font-lock-declarations
signals to c-forward-decl-or-cast-1 that point is at the top level.

* lisp/progmodes/cc-langs.el (c-get-state-before-change-functions): add
c-truncate-bs-cache.
(c-flat-decl-block-kwds, c-brace-stack-thing-key, c-brace-stack-no-semi-key)
(c-type-decl-operator-prefix-key): new language constants/variables.

* lisp/progmodes/cc-engine.el (c-bs-interval, c-bs-cache, c-bs-cache-limit)
(c-bs-prev-pos, c-bs-prev-stack): New mostly local variables for the brace
stack cache.
(c-init-bs-cache, c-truncate-bs-cache, c-truncate-bs-cache, c-brace-stack-at)
(c-bs-at-toplevel-p): New functions which manipulate the brace stack (cache).
(c-find-decl-prefix-search): Keep track of whether we're at top level.
(c-find-decl-spots): New local variable cfd-top-level which records what it
says.  On calling cfd-fun, pass cfd-top-level as an additional argument.
(c-forward-declarator): Add new element DECORATED to the result list.  Set it
to non-nil when a match for c-type-decl-operator-prefix-key is found.
(c-forward-decl-or-cast-1): Handle the newly introduced context "top".
Introduce "CASE 9.5", which recognizes direct initializations.

* lisp/progmodes/cc-fonts.el (c-font-lock-complex-decl-prepare)
(c-font-lock-enum-tail, c-font-lock-cut-off-declarators)
(c-font-lock-enclosing-decls, c-simple-decl-matchers, c-basic-matchers-after):
Add appropriate `not-top' argument to calls to c-font-lock-declarators.
(c-font-lock-declarators): Additional parameter `not-top'.  Use not-top to
participate in the decision whether to fontify an identifier as a function or
a variable.
(c-font-lock-declarations): The internal lambda function takes an additional
argument `toplev' from c-find-decl-spots, which it uses in determining the
"context" of a declaration.  Add appropriate `not-top' argument to calls to
c-font-lock-declarators.
(c-font-lock-objc-methods): Add extra parameter to internal lambda function,
like for c-font-lock-declarators.

* lisp/progmodes/cc-mode.el (c-basic-common-init): Initialize the brace stack
cache.