Bug: expand autocmd with <abuf> is wrong for BufUnload

  @Autocmd('BufUnload', {
    sync: true,
    pattern: '*',
    eval: 'expand("<abuf>")'
  })
  public async onBufUnload(bufnr: string):Promise<void> {
    logger.debug(`file: ${bufnr} remove`)
  }

The bufnr here is always the buffer number of current buffer number, but it should be the buffer number of removed buffer.

autocmd BufUnload * call s:OnUnload()
function! s:OnUnload()
  echo +expand('<abuf>')
endfunction

vim script doesn't have this problem.

BTW: <afile> is neither correct.

Start at the TypeScript @Autocmd entry point and trace how eval: 'expand("")' is evaluated for BufUnload; compare it with the Vimscript example and the case. Done when unload callbacks receive the removed buffer and file values rather than the current buffer, with regression coverage for both cases.