patch 9.0.1951: Vim9: hard to debug vim9_class errors from CI

Problem:  Vim9: hard to debug vim9_class errors from CI
Solution: Include the line number in assert_xxx() calls.  Include the
          entire error message in the tests.  Fix the indentation in the
          test file.  Add tags for new error codes.

closes: #13206

Signed-off-by: Christian Brabandt <cb@256bit.org>
Co-authored-by: Yegappan Lakshmanan <yegappan@yahoo.com>
diff --git a/runtime/doc/vim9class.txt b/runtime/doc/vim9class.txt
index 5cbdc72..6b51e86 100644
--- a/runtime/doc/vim9class.txt
+++ b/runtime/doc/vim9class.txt
@@ -258,10 +258,15 @@
 step the object variables of the parent class are initialized first.  There is
 no need to call "super()" or "new()" on the parent.
 
-						*E1365*
+							*E1365*
 When defining the new() method the return type should not be specified.  It
 always returns an object of the class.
 
+							*E1386*
+When invoking an object method, the method name should be preceded by the
+object variable name.  A object method cannot be invoked using the class
+name.
+
 ==============================================================================
 
 3.  Class Variables and Methods			*Vim9-class-member*
@@ -282,7 +287,7 @@
 Since the name is used as-is, shadowing the name by a method argument name
 or local variable name is not allowed.
 
-							*E1374* *E1375*
+					    *E1374* *E1375* *E1384* *E1385*
 To access a class member outside of the class where it is defined, the class
 name prefix must be used.  A class member cannot be accessed using an object.