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

runtime/lua/vim/_meta/api_keysets_extra.lua

@@ -111,7 +111,7 @@ error('Cannot require a meta file')
 ---
 --- Command modifiers in a structured format. Has the same structure as the
 --- "mods" key of |nvim_parse_cmd()|.
---- @field smods table
+--- @field smods vim.api.keyset.cmd_mods
 
 --- @class vim.api.keyset.command_info
 --- @field name string