Upgrade antd v5

• upgrade antd library to version 5
• remove obsolete import 'antd/dist/antd.less' (file no longer exists)
• delete antd-theme-webpack-plugin, its usage in webpack config, and LessVariablesRemapper as they are no longer needed to apply a custom theme
• apply theme via the ConfigProvider
• set font size in the dev app to 16px; all three variables below need to be set so that the font size is applied consistently and without unintended side effects:

  fontSize: '16',
  lineHeight: '1.618',
  fontSizeBase: '16px',

Unlocks upgrading to antd v5 in hhmi