patch 8.2.2305: Vim9: "++var" and "--var" are silently accepted

Problem:    Vim9: "++var" and "--var" are silently accepted.
Solution:   Give an error message.

patch 8.2.2304: Vim9: no test for unletting an imported variable

Problem:    Vim9: no test for unletting an imported variable.
Solution:   Add a test.  Fix line number in error.

patch 8.2.2303: Vim9: backtick expansion doesn't work for :foldopen

Problem:    Vim9: backtick expansion doesn't work for :foldopen.
Solution:   Do recognize backtick expansion. (closes vim#7621)

patch 8.2.2302: Vim9: using an option value may use uninitialized memory

Problem:    Vim9: using an option value may use uninitialized memory.
Solution:   Clear v_lock. (closes vim#7620)

patch 8.2.2301: Vim9: cannot unlet a dict or list item

Problem:    Vim9: cannot unlet a dict or list item.
Solution:   Add ISN_UNLETINDEX.  Refactor assignment code to use for unlet.

patch 8.2.2300: Vim9: wrong order on type stack when using dict

Problem:    Vim9: wrong order on type stack when using dict.
Solution:   Generate constants before a dict. (closes vim#7619)

patch 8.2.2299: Vim9: invalid memory access making error message flaky

Problem:    Vim9: invalid memory access making error message flaky.
Solution:   Do not check cmd_argt for CMD_USER. (issue vim#7467)

patch 8.2.2298: Vim9: comment right after "(" of function not recognized

Problem:    Vim9: comment right after "(" of function not recognized.
Solution:   Do not skip over white space before calling get_function_args().
            (closes vim#7613)

patch 8.2.2297: Vim9: cannot set 'number' to a boolean value

Problem:    Vim9: cannot set 'number' to a boolean value.
Solution:   Use tv_get_bool(). (closes vim#7615)

patch 8.2.2296: cannot use CTRL-N and CTRL-P in a popup menu

Problem:    Cannot use CTRL-N and CTRL-P in a popup menu.
Solution:   Use CTRL-N like <Down> and CTRL-P like <Up>. (closes vim#7614)