Problem:    The code style has to be checked manually.
Solution:   Add basic code style checks in a test.  Fix or avoid uncovered
            problems.

Problem:    Completion of :runtime does not handle {where} argument.
Solution:   Parse the {where} argument. (closes #11863)

Problem:    No cmdline completion for :runtime.
Solution:   Add completion for :runtime. (closes #11853, closes #11447)
            Improve the resulting matches.

Problem:    Crash when using kitty and using a mapping with <Esc>.
Solution:   Do not try setting did_simplify when it is NULL. (closes #11817)

Problem:    Return value of type() for class and object unclear.
Solution:   Add v:t_object and v:t_class.

Problem:    :interface is not implemented yet.
Solution:   Implement the basics of :interface.

Problem:    Cannot define a method in a class.
Solution:   Implement defining an object method.  Make calling an object
            method work.

Problem:    Vim9 class is not implemented yet.
Solution:   Add very basic class support.

Problem:    Cannot debug the Kitty keyboard protocol with TermDebug.
Solution:   Add Kitty keyboard protocol support to the libvterm fork.
            Recognize the escape sequences that the protocol generates.  Add
            the 'keyprotocol' option to allow the user to specify for which
            terminal what protocol is to be used, instead of hard-coding this.
            Add recognizing the kitty keyboard protocol status.

Problem:    The WinScrolled autocommand event is not enough.
Solution:   Add WinResized and provide information about what changed.
            (closes #11576)