patch 9.0.1909: Vim9: problem calling class method from other class

Problem:  Vim9: problem calling class method from other class
Solution: Fix this problem, fix readonly object access, update error
          messages.

Calling a class method from another method without the class name prefix
doesn't work properly.

A readonly object variable is modifiable outside the class using a
nested object assignment.

Remove the unused E1338 error message.

Update error messages.

closes: #13116

Signed-off-by: Christian Brabandt <cb@256bit.org>
Co-authored-by: Yegappan Lakshmanan <yegappan@yahoo.com>
diff --git a/src/version.c b/src/version.c
index 18c12fa..7670cdd 100644
--- a/src/version.c
+++ b/src/version.c
@@ -700,6 +700,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1909,
+/**/
     1908,
 /**/
     1907,