allow to force installing a clangd and qtcreator files

Add a forceclangd target to Makefile to force installing a .clangd file.
Add a forceqtcreator target to force installing qtcreator files.
Existing files will be overwritten.

while here:
- update the c++ standard to c++23

.templates/install_clangd.sh

@@ -5,6 +5,14 @@ GLOBAL_WORKING_DIR=$(realpath ${CURRENT_DIR}/..)
 
 # ----------
 
+has_force_arg=0
+
+if [ $# -eq 1 ] ; then
+	if [ $1 == 'force' ] ; then
+		has_force_arg=1
+	fi
+fi
+
 # make sure the current directory is correct
 if [ ! -d ${CURRENT_DIR}/.templates ] ; then
 	echo "this script should be called by make: make clangd (one level up)"
@@ -17,7 +25,7 @@ GLOBAL_WORKING_DIR_FOR_SED=$(echo ${GLOBAL_WORKING_DIR} | sed 's/\//\\\//g')
 
 
 if [ -f "${CURRENT_DIR}/.templates/.clangd" ] ; then
-	if [ ! -f "${CURRENT_DIR}/.clangd" ] ; then
+	if [ $has_force_arg -eq 1 -o ! -f "${CURRENT_DIR}/.clangd" ] ; then
 		cat "${CURRENT_DIR}/.templates/.clangd" | \
 			sed -e "s/%%%CURRENT_DIR%%%/${CURRENT_DIR_FOR_SED}/g" \
 				-e "s/%%%GLOBAL_WORKING_DIR%%%/${GLOBAL_WORKING_DIR_FOR_SED}/g" > \