Problem:    Function name does not match autocmd event name.
Solution:   Rename "optionsset" to "optionset". (closes #11630)

Problem:    Virtual text below cannot be placed below empty lines.
Solution:   Add one character. (James Alvarado, closes #11606, closes #11520)

Problem:    Using deletebufline() may jump to another window.
Solution:   Do not use a window where the buffer was only in the past.
            (closes #11594)

Problem:    Error when using the "Tools / Spelling / Find More Languages"
            menu.
Solution:   Remove "<SID>".  Reset "g:menutrans_set_lang_to" when 'encoding'
            changes. (closes #11625)

Problem:    Error when using the "File Settings / Text Width" menu.
Solution:   Use str2nr(). (closes #11624)

Problem:    Messages test is flaky.
Solution:   Add a short delay.

Problem:    Tests fail without the terminal feature.
Solution:   Move functions to another utility script.

Problem:    Terminal tests fail when using key with modifier.
Solution:   Use the modifyOtherKeys encoding when using RunVimInTerminal().

Problem:    Libvterm does not support the XTQMODKEYS request.
Solution:   Implement the XTQMODKEYS request and response.  Update the keycode
            check results.

Problem:    Cannot detect whether modifyOtherKeys is enabled.
Solution:   Use XTQMODKEYS introduced by xterm version 377 to request the
            modifyOtherKeys level.  Update the keycode check results.