getIconsPrefix (theme) {
    return {
      bootstrap3: 'glyphicon',
      bootstrap4: 'fa',
      bootstrap5: 'bi',
      'bootstrap-table': 'icon',
      bulma: 'fa',
      foundation: 'fa',
      materialize: 'material-icons',
      semantic: 'fa'
    }[theme] || 'fa'
  }
Returns the prefix for the icons based on the theme.

@param {string} theme - The theme name (bootstrap3, bootstrap4, bootstrap5, bootstrap-table, bulma, foundation, materialize, semantic).
@returns {string} The icons prefix.