patch 9.0.1031: Vim9 class is not implemented yet

Problem:    Vim9 class is not implemented yet.
Solution:   Add very basic class support.
diff --git a/src/vim.h b/src/vim.h
index 67751ff..e241da0 100644
--- a/src/vim.h
+++ b/src/vim.h
@@ -2120,6 +2120,8 @@
 #define VAR_TYPE_CHANNEL    9
 #define VAR_TYPE_BLOB	    10
 #define VAR_TYPE_INSTR	    11
+#define VAR_TYPE_CLASS	    12
+#define VAR_TYPE_OBJECT	    13
 
 #define DICT_MAXNEST 100	// maximum nesting of lists and dicts