reorganize so that initialization is done in lua

`: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.

Neovim currently places its own loader for searching runtime files at
the front of `package.loaders`. This prevents any preloaders in
`package.preload` from being used. This change fixes that by moving the
default package preloader to run before Neovim's loader. For example,
LuaJIT provides preloaders for the built-in modules `ffi` and `bit`, so
this optimisation will improve the loading of those.

Like vim.notify(), but only displays the notification once.

This introduces two new functions `vim.keymap.set` & `vim.keymap.del`

differences compared to regular set_keymap:
- remap is used as opposite of noremap. By default it's true for <Plug> keymaps and false for others.
- rhs can be lua function.
- mode can be a list of modes.
- replace_keycodes option for lua function expr maps. (Default: true)
- handles buffer specific keymaps

Examples:
```lua
vim.keymap.set('n', 'asdf', function() print("real lua function") end)
vim.keymap.set({'n', 'v'}, '<leader>lr', vim.lsp.buf.references, {buffer=true})
vim.keymap.set('n', '<leader>w', "<cmd>w<cr>", {silent = true, buffer = 5 })
vim.keymap.set('i', '<Tab>', function()
  return vim.fn.pumvisible() == 1 and "<C-n>" or "<Tab>"
end, {expr = true})
vim.keymap.set('n', '[%', '<Plug>(MatchitNormalMultiBackward)')

vim.keymap.del('n', 'asdf')
vim.keymap.del({'n', 'i', 'v'}, '<leader>w', {buffer = 5 })
```

Adds a new vim.filetype module that provides support for filetype detection in
Lua.

Co-authored-by: Gregory Anders <8965202+gpanders@users.noreply.github.com>
Co-authored-by: Evgeni Chasnovski <evgeni.chasnovski@gmail.com>
Co-authored-by: zeertzjq <zeertzjq@outlook.com>
Co-authored-by: Christoph Hasse <hassec@users.noreply.github.com>
Co-authored-by: Alef Pereira <ealefpereira@gmail.com>
Co-authored-by: AusCyber <willp@outlook.com.au>
Co-authored-by: kylo252 <59826753+kylo252@users.noreply.github.com>