Problem:
Not all Lua code is checked by stylua. Automating code-style is an
important mechanism for reducing time spent on accidental
(non-essential) complexity.
Solution:
- Enable lintlua for `test/unit/` directory.
- TODO: only `test/functional/` remains unchecked.
previous: 45fe4d11ad
previous: 517f0cc634
- Move vimoption_T to option.h
- option_defs.h is for option-related types
- option_vars.h corresponds to Vim's option.h
- option_defs.h and option_vars.h don't include each other
The test.functional.helpers and test.unit.helpers modules now include
all of the public functions from test.helpers, so there is no need to
separately require('test.helpers').
