buffer: consistent error for length > kMaxLength

- Always return the same error message(hopefully more informative)
  for buffer length > kMaxLength and avoid getting into V8 C++ land
  for unnecessary checks.
- Use accurate RegExp(reusable as `common.bufferMaxSizeMsg`)
  in tests for this error.
- Separate related tests from test-buffer-alloc.

PR-URL: https://github.com/nodejs/node/pull/10152


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>