Add menu ID argument to `wp_page_menu()` so that fallback menus have same attributes as `wp_nav_menu()`

[lancewillett]

See use case in Twenty Fourteen menu behavior: https://core.trac.wordpress.org/ticket/31527#comment:25

When no custom menu is set, the menu doesn't output the HTML ID attribute on the div element that wraps the pages menu.

This means things like accessibility attributes (like ARIA targets) don't work because the ID is missing from the HTML output.

[lancewillett]

Patch also sanitizes both class and ID values before outputting them.

[lancewillett]

Please reference #31527 when this goes in.

[ocean90]

Without sanitize_html_class()

[ocean90]

I don't think that sanitize_html_class() is needed. This could lead to regressions since it's possible to define multiple CSS classes. The id attribute should be before the class attribute.
Also the current patch will print an empty id attribute by default. That should be avoided.

Punting per bug scrub.

[wonderboymusic]

In 34330:

Add a 'menu_id' argument to wp_page_menu() so that fallback menus have the same attributes as wp_nav_menu().

Props lancewillett, ocean90, wonderboymusic.
Fixes #31656.

[obenland]

Unfortunately [34330] breaks back compat with themes that rely on the id to be missing from wp_page_menu() to style the fallback menu accurately. We should consider reverting.

[lancewillett]

I think we should keep the change — and help theme authors learn how to style the fallback in a better way, maybe with a educational post in the handbook.

[obenland]

I'm fine with more education rather than reverting and I reached out to @davidakennedy for a make/core post. Also see ​chat on Slack.