Link "widget areas" to widgets panel in menu locations section description

[celloexpressions]

In the menus panel description, the text "widget areas" is linked to the widgets panel and conditional on the theme supporting widgets. This should also be the case for the menu locations section description. The text is currently incorrectly displayed for themes that don't support widgets.

This would be a good opportunity to use the new focusConstructAndReturnToControlWhenCollapsed function introduced in #32683, although this is tied to a section, not a control, so perhaps it should be generalized to focusConstructAndReturnWhenCollapsed and added to sections and panels as well. Let's finalize that on #32683, then revisit here.

[celloexpressions]

Actually, I don't think it's necessary to keep a breadcrumb here, so 36796.diff​ should work (and matches what the panel does).

[lukecavanagh]

Ends up causing

Parse error: syntax error, unexpected 'public' (T_PUBLIC) in /srv/www/wordpress-trunk/wp-includes/class-wp-customize-nav-menus.php on line 639

[celloexpressions]

@lukecavanagh are you sure the patch applied correctly? public doesn't appear in the patch, although maybe there's a missing semicolon or something?

[lukecavanagh]

@celloexpressions I will clean up my local WP and apply the patch again, just to check.

[lukecavanagh]

@celloexpressions patch applied fine, without any errors and customizer loads fine. This was using TwentySixteen as the active theme on the local dev site.

[celloexpressions]

Re-tested the patch an it still works fine for me, can someone else check it?

[monikarao]

Just tested the patch and it works fine for me.
OS: Windows 10
Browser: Chrome 50.0.2661.102 , Safari 5.1.7 , IE-11 , Firefox 46.0.1
WP 4.5.2 , 4.5.3-alpha-37528
Server Environment : VVV

[celloexpressions]

Ready for final review.

[ocean90]

In 37900:

Customize: Link "widget areas" to widgets panel in menu locations section description.

Props celloexpressions.
Fixes #36796.