new loplugin:namespaceindentation

check indentation of braces in namespace decls,
and the comments that often appear with them.

This is my penance for messing up the indentation with
clang-tidy-modernize-namespaces.

As such I have limited it to new-style namespaces for now,
and the check is off by default.

Change-Id: I4db7f10a81c79bc0eece8f8e3ee564da8bc7f168
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/87723
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>

cppcanvas/source/mtfrenderer/implrenderer.cxx

@@ -229,7 +229,7 @@ namespace
 }
 
 namespace cppcanvas::internal
-    {
+{
         // state stack manipulators
 
         void VectorOfOutDevStates::clearStateStack()
@@ -3069,6 +3069,6 @@ namespace cppcanvas::internal
                 return false;
             }
         }
-    }
+}
 
 /* vim:set shiftwidth=4 softtabstop=4 expandtab: */