Adding priority to individual settings via the settings API.

[alexmansfield]

Currently there is no way (at least that I could find) to specify the order of settings on a settings page (for example, a theme options page). Use case: a child theme adding a setting to the parent theme's "Theme Options" page has no way of specifying the order in which the new setting should be inserted.

I've modified the add_settings_field() function to allow for a priority to be set (much like when adding settings to the theme customizer). I also added uasort($wp_settings_fields[$page][$section], 'compare_priority'); to the do_settings_fields() function, where 'compare_priority' is a slightly modified version of the compare function used to set the priority of the theme customizer sections.

This patch is loosely related to #22487 which adds priority to settings sections, but not individual settings.

Adds priority option to individual settings