patch 9.0.1885: Vim9: no support for abstract methods

Problem:  Vim9: no support for abstract methods
Solution: Add support for defining abstract methods in an abstract class

closes: #13044
closes: #13046

Signed-off-by: Christian Brabandt <cb@256bit.org>
Co-authored-by: Yegappan Lakshmanan <yegappan@yahoo.com>
diff --git a/src/userfunc.c b/src/userfunc.c
index 6638849..efde29d 100644
--- a/src/userfunc.c
+++ b/src/userfunc.c
@@ -5021,6 +5021,7 @@
     // Do not define the function when getting the body fails and when
     // skipping.
     if (((class_flags & CF_INTERFACE) == 0
+		&& (class_flags & CF_ABSTRACT_METHOD) == 0
 		&& get_function_body(eap, &newlines, line_arg, lines_to_free)
 								       == FAIL)
 	    || eap->skip)