feat(lua): show proper verbose output for lua configuration

`:verbose` didn't work properly with lua configs (For example:
    options or keymaps are set from lua, just say that they were set
    from lua, doesn't say where they were set at.

This fixes that issue. Now `:verbose` will provide filename and line no
when option/keymap is set from lua.

Changes:
  - compiles lua/vim/keymap.lua as vim/keymap.lua
 - When souring a lua file current_sctx.sc_sid is set to SID_LUA
 - Moved finding scripts SID out of `do_source()` to `get_current_script_id()`.
   So it can be reused for lua files.
 - Added new function `nlua_get_sctx` that extracts current lua scripts
   name and line no with debug library. And creates a sctx for it.
     NOTE: This function ignores C functions and blacklist which
     currently contains only vim/_meta.lua so vim.o/opt wrappers aren't
     targeted.
 - Added function `nlua_set_sctx` that changes provided sctx to current
   lua scripts sctx if a lua file is being executed.
 - Added tests in tests/functional/lua/verbose_spec.lua
 - add primary support for additional types (:autocmd, :function, :syntax) to lua verbose
    Note: These can't yet be directly set from lua but once that's possible
    :verbose should work for them hopefully :D
 - add :verbose support for nvim_exec & nvim_command within lua
    Currently auto commands/commands/functions ... can only be defined
    by nvim_exec/nvim_command this adds support for them. Means if those
    Are defined within lua with vim.cmd/nvim_exec :verbose will show their
    location . Though note it'll show the line no on which nvim_exec call was made.

src/nvim/lua/vim.lua

@@ -43,6 +43,9 @@ assert(vim.inspect)
 vim.filetype = package.loaded['vim.filetype']
 assert(vim.filetype)
 
+vim.keymap = package.loaded['vim.keymap']
+assert(vim.keymap)
+
 -- These are for loading runtime modules lazily since they aren't available in
 -- the nvim binary as specified in executor.c
 setmetatable(vim, {
@@ -69,9 +72,6 @@ setmetatable(vim, {
     elseif key == 'ui' then
       t.ui = require('vim.ui')
       return t.ui
-    elseif key == 'keymap' then
-      t.keymap = require('vim.keymap')
-      return t.keymap
     end
   end
 })