Change Gravity Forms <input> into a <button> while preserving attributes and custom submit text.

gf_make_submit_input_into_a_button_element.php

function gf_make_submit_input_into_a_button_element($button_input, $form) {
  preg_match("/<input([^\/>]*)(\s\/)*>/", $button_input, $button_match);
  $button_atts = str_replace("value='".$form['button']['text']."' ", "", $button_match[1]);
  return '<button '.$button_atts.'>'.$form['button']['text'].'<i class="fa fa-refresh"></i></button>';
}
add_filter('gform_submit_button', 'gf_make_submit_input_into_a_button_element', 10, 2);