Problem:
- nvim_subscribe, nvim_unsubscribe were deprecated in
  aec4938a21a02d279d13a9eb64ef3b7cc592c374 but this wasn't set in the
  API metadata.
- The function annotations
  ```
  FUNC_API_SINCE(1) FUNC_API_REMOTE_ONLY FUNC_API_DEPRECATED_SINCE(13)
  ```
  cause this test to fail:
   ```
   RUN T3 api metadata functions are compatible with old metadata or have new level: 3.00 ms ERR
   test/functional/api/version_spec.lua:135: function vim_subscribe was removed but exists in level 0 which nvim should be compatible with
   stack traceback:
     test/functional/api/version_spec.lua:135: in function <test/functional/api/version_spec.lua:128>
   ```

Solution:
- Set the API metadata.
- Rearrange the annotations so that FUNC_API_DEPRECATED_SINCE is 2nd:
  ```
  FUNC_API_SINCE(1) FUNC_API_DEPRECATED_SINCE(13) FUNC_API_REMOTE_ONLY
  ```

Problem:  Lua callbacks for "msg_show" events with vim.ui_attach() are
          executed when it is not safe.
Solution: Disallow non-fast API calls for "msg_show" event callbacks.
          Automatically detach callback after excessive errors.
          Make sure fast APIs do not modify Nvim state.

In the api_info() output:

    :new|put =map(filter(api_info().functions, '!has_key(v:val,''deprecated_since'')'), 'v:val')
    ...

    {'return_type': 'ArrayOf(Integer, 2)', 'name': 'nvim_win_get_position', 'method': v:true, 'parameters': [['Window', 'window']], 'since': 1}

The `ArrayOf(Integer, 2)` return type didn't break clients when we added
it, which is evidence that clients don't use the `return_type` field,
thus renaming Dictionary => Dict in api_info() is not (in practice)
a breaking change.

This also makes shada reading slightly faster due to avoiding
some copying and allocation.

Use keysets to drive decoding of msgpack maps for shada entries.

fixes #28782 (when backported)

There's no "rule" or bad practice or whatever that says we cannot
generate c files. it is is just that we have ~20 generated headers
and ~2 generated sources and there is nothing in these two generated
source files which sets them aparts. Lua bindings are not different from
rpc bindings, and pathdef is not different from versiondef.

So to simplify build logic and ease the future port to build.zig,
streamline the build to only have generated headers, no direct generated
.c files.

Also "nlua_add_api_functions" had its prototype duplicated twice which
defeated the point of having mandatory prototypes (one source of truth).

Co-authored-by: C.D. MacEachern <craig.daniel.maceachern@gmail.com>
Co-authored-by: Ynda Jas <yndajas@gmail.com>
Co-authored-by: Owen Hines <TheOdd@users.noreply.github.com>
Co-authored-by: Wanten <41904684+WantenMN@users.noreply.github.com>
Co-authored-by: lukasvrenner <118417051+lukasvrenner@users.noreply.github.com>
Co-authored-by: cuinix <915115094@qq.com>