feat(vimfn): use Lua for more excmds/vimfns

Problem:
Too much boilerplate needed to use Lua to impl an excmd or f_xx
function.

Solution:
- Add `nlua_call_vimfn` which takes the args typval, executes
  Lua, and returns a typval.
- refactor(excmd): lua impl for :log, :lsp

scripts/linterrcodes.lua

@@ -48,7 +48,7 @@ local dup_allowed = {
   E509 = 2,
   E5101 = 2,
   E5102 = 2,
-  E5108 = 4,
+  E5108 = 6,
   E5111 = 2,
   E513 = 2,
   E521 = 2,