Vim9 class/object member access control

[Yegappan Lakshmanan]

Hi all,

The access control to readonly, read-write and private members in a
class/object discussed in https://github.com/vim/vim/discussions/12979
should all work now. Let us know if there are any cases where the
access control is not correctly enforced.

When testing these, I found an existing memory corruption issue
with class member variables. When a class member uses a complex
type (e.g. List or Dict), then it is garbage collected under some
conditions leading to a memory corruption (reported by ASAN and
Valgrind). I am still debugging this issue.

Regards,
Yegappan

[Yegappan Lakshmanan]

Correction: This is a use-after-free problem and not a memory corruption.

- Yegappan