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
Note: formatc.lua was unable to swallow some newer additions to ExprASTNodeType
(specifically `kExprNodeOr = '|'` and probably something else), so all `= …`
were dropped: in any case they only were there in order to not bother updating
viml_pexpr_debug_print_ast_node and since it is now known all nodes which will
be present it is not much of an issue.
