llama.vim : add classic vim support (#9995)

* added classic vim support

* fixed ring update, removed blank line

* minor

* minor

* minor doc update

* removed uneeded var

* minor

* minor

* fixed job_start creating new scratch buffers

* fixed job_start creating new scratch buffers

* fixed ghost text indenting when expandtab is on

* removed unused code

* minor

* unified fim_on_exit

* minor

* vim ghost text rendering now uses pos_x and pos_y parameters

* renamed *_hlgroup to hlgroup_*

* renamed *_ghost_text to ghost_text_*, moved nvim/vim detection to llama#init()

* minor

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Co-authored-by: Michael Coppola <info@michaeljcoppola.com>