feat(lsp)!: remove client-server handlers from vim.lsp.handlers

- Partition the handlers in vim.lsp.handlers as:
  - client to server response handlers (RCS)
  - server to client request handlers (RSC)
  - server to client notification handlers (NSC)

  Note use string indexes instead of protocol.methods for improved
  typing in LuaLS (tip: use hover on RCS, RSC or NSC).

runtime/lua/vim/lsp.lua

@@ -1165,6 +1165,7 @@ function lsp.for_each_buffer_client(bufnr, fn)
   end
 end
 
+--- @deprecated
 --- Function to manage overriding defaults for LSP handlers.
 ---@param handler (lsp.Handler) See |lsp-handler|
 ---@param override_config (table) Table containing the keys to override behavior of the {handler}