CC Mode: Don't indent a construct in a class after a template

This fixes bug#79438.

* lisp/progmodes/cc-align.el (c-lineup-class-field-cont): New
function.

* lisp/progmodes/cc-vars.el (c-offsets-alist): Change the
entry for class-field-cont from + to
c-lineup-class-field-cont.

* doc/misc/cc-mode.texi (Misc Line-Up): Add a new entry for
c-lineup-class-field-cont.

doc/misc/cc-mode.texi

@@ -6992,6 +6992,18 @@ the_larch,            @hereFn{c-lineup-topmost-intro-cont}
 @workswith @code{topmost-intro-cont}.
 @end defun
 
+@comment ------------------------------------------------------------
+
+@defun c-lineup-class-field-cont
+@findex lineup-class-field-cont (c-)
+Indent continutation lines zero or one @code{c-basic-offset} steps.
+This is intended for continuation lines within a class/struct
+etc. construct.  For a declaration following a template specification,
+zero steps are used.  Other constructs are indented one step.
+
+@workswith @code{class-field-cont}.
+@end defun
+
 @comment !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
 @node    Custom Line-Up
 @section Custom Line-Up Functions

lisp/progmodes/cc-align.el

@@ -97,6 +97,16 @@ Works with: topmost-intro-cont."
 			    t))))
 	  c-basic-offset))))
 
+(defun c-lineup-class-field-cont (langelem)
+  "Line up continuation lines in a class zero or one indentation steps.
+For a declaration following a template specification, zero steps are
+used.  Other constructs are indented one step."
+  (save-excursion
+    (beginning-of-line)
+    (c-backward-syntactic-ws (c-langelem-pos langelem))
+    (unless (eq (char-before) ?>)
+      c-basic-offset)))
+
 (defun c-lineup-gnu-DEFUN-intro-cont (langelem)
   "Line up the continuation lines of a DEFUN macro in the Emacs C source.
 These lines are indented `c-basic-offset' columns, usually from column 0.

lisp/progmodes/cc-vars.el

@@ -1302,7 +1302,7 @@ can always override the use of `c-default-style' by making calls to
        ;; Anchor pos: Boi at the func decl arglist open.
        (member-init-cont      . c-lineup-multi-inher)
        ;; Anchor pos: Beg of the first member init.
-       (class-field-cont      . +)
+       (class-field-cont      . c-lineup-class-field-cont)
        ;; Anchor pos: BOI of the line containing the class keyword.
        ;; 2nd pos: At the open brace.
        (inher-intro           . +)