Most of the `tabindex` attributes across the admin were removed in [21311].
This commit updates the example for the `$other_attributes` parameter to use the `id` attribute instead.
Includes synchronizing documentation between `submit_button()` and `get_submit_button()`.
Follow-up to [15810], [16061], [21311], [27136], [31599].
Props benjaminknox, sabernhardt, fushar, SergeyBiryukov.
Fixes#59768.
Built from https://develop.svn.wordpress.org/trunk@57114
git-svn-id: http://core.svn.wordpress.org/trunk@56625 1a063a9b-81f0-0310-95a4-ce76da25c4cd