fix(api,lsp): call on_detach before wiping out the buffer #35355

Problem:
Buffer-updates on_detach callback is invoked before buf_freeall(), which
deletes autocmds of the buffer (via apply_autocmds(EVENT_BUFWIPEOUT,
...)). Due to this, buffer-local autocmds executed in on_detach (e.g.,
LspDetach) are not actually invoked.

Solution:
Call buf_updates_unload() before buf_freeall().

src/nvim/buffer.c

@@ -656,6 +656,10 @@ bool close_buffer(win_T *win, buf_T *buf, int action, bool abort_if_last, bool i
 
   buf->b_nwindows = nwindows;
 
+  // Disable buffer-updates for the current buffer.
+  // No need to check `unload_buf`: in that case the function returned above.
+  buf_updates_unload(buf, false);
+
   buf_freeall(buf, ((del_buf ? BFA_DEL : 0)
                     + (wipe_buf ? BFA_WIPE : 0)
                     + (ignore_abort ? BFA_IGNORE_ABORT : 0)));
@@ -678,10 +682,6 @@ bool close_buffer(win_T *win, buf_T *buf, int action, bool abort_if_last, bool i
     return false;
   }
 
-  // Disable buffer-updates for the current buffer.
-  // No need to check `unload_buf`: in that case the function returned above.
-  buf_updates_unload(buf, false);
-
   if (win != NULL  // Avoid bogus clang warning.
       && win_valid_any_tab(win)
       && win->w_buffer == buf) {