patch 8.2.1898: command modifier parsing always uses global cmdmod

Problem:    Command modifier parsing always uses global cmdmod.
Solution:   Pass in cmdmod_T to use.  Rename struct fields consistently.
diff --git a/src/change.c b/src/change.c
index 44c2f04..4578057 100644
--- a/src/change.c
+++ b/src/change.c
@@ -453,7 +453,7 @@
 #endif
 
     // set the '. mark
-    if (!cmdmod.keepjumps)
+    if ((cmdmod.cmod_flags & CMOD_KEEPJUMPS) == 0)
     {
 	curbuf->b_last_change.lnum = lnum;
 	curbuf->b_last_change.col = col;