runtime(lf): improve syntax script, add filetype plugin

runtime(lf): improve syntax script, add filetype plugin

- Greatly improve detection and highlighting of command/shell regions,
  input-device key labels, escape sequences (@joelim-work)
- Add ftplugin for formatoptions, toggling comment areas
  (@andis-sprinkis)
- Add a few missing lf option keywords, rm. old non-working code, misc.
  formatting (@andis-sprinkis)

closes: #17078

Signed-off-by: Andis Spriņķis <andis@sprinkis.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>