CC Mode: Add second anchor point to class-open and class-close

CC Mode: Add second anchor point to class-open and class-close

This fixes the second (last) part of bug#66911.  The new second
anchor points allow the indentation of braces in template
classes to be anchored on the keyword 'class' rather than the
`template' at the beginning of the statement.

* lisp/progmodes/cc-engine.el (c-add-class-syntax): Add &rest
args parameter for additional anchor points.  Pass these to
c-add-syntax.
(c-guess-continued-construct): CASE B.1: Note return value from
c-looking-at-decl-block and pass this to c-add-syntax for a
class-open construct.
(c-guess-basic-syntax): CASE 4: Duplicate anchor position for
class-open.
(c-guess-basic-syntax): CASE 5A.2: Note return value of
c-looking-at-decl-block and pass it as extra argument to
c-add-syntax for a class-open construct.
(c-guess-basic-syntax): CASE 5G: Call c-looking-at-decl-block
to determine the second anchor point for a class-close, and
pass it to c-add-class-syntax.

* doc/misc/cc-mode.texi (Class Symbols): Document the anchor
points for class-open and class-close.