patch 8.2.3190: error messages are spread out

Problem:    Error messages are spread out.
Solution:   Move error messages to errors.h and give them a clear name.
diff --git a/src/time.c b/src/time.c
index eeefeb6..f7f614e 100644
--- a/src/time.c
+++ b/src/time.c
@@ -757,7 +757,7 @@
     if (argvars[0].v_type != VAR_UNKNOWN)
     {
 	if (argvars[0].v_type != VAR_NUMBER)
-	    emsg(_(e_number_exp));
+	    emsg(_(e_number_expected));
 	else
 	{
 	    timer = find_timer((int)tv_get_number(&argvars[0]));
@@ -783,7 +783,7 @@
 	return;
 
     if (argvars[0].v_type != VAR_NUMBER)
-	emsg(_(e_number_exp));
+	emsg(_(e_number_expected));
     else
     {
 	int	paused = (int)tv_get_bool(&argvars[1]);
@@ -844,7 +844,7 @@
 
     if (argvars[0].v_type != VAR_NUMBER)
     {
-	emsg(_(e_number_exp));
+	emsg(_(e_number_expected));
 	return;
     }
     timer = find_timer((int)tv_get_number(&argvars[0]));