Toolbar links unexpectedly take you to different contexts

[helen]

Spinning off from #32678 for something addressable in 4.3:

Right now, some links take you into the customizer context without warning (as do a couple in the admin menu), which is quite jarring. We need context for each link to be clearer

[helen]

Wide view

[helen]

Mid width view

[helen]

Narrow view

[helen]

32924.diff​ adds a top level Customize item between the site name and update items. The site name submenu now only contains links to the dashboard - Dashboard, Themes, Widgets, and Menus. Header and Background are still in there as links to the old admin screens for when the customizer is not available, as before. We need to hide an item at < 400px wide, I chose add new in the patch but comments may be better. Screenshots above, sorry for the crazy header image.

Edit: The plus icon is fixed now, I didn't notice that it was still with the wrong one when I took the screenshots.

[helen]

In 33130:

Toolbar: Disambiguate links to the dashboard vs. to the customizer.

All links in the site name menu now point to admin screens, and Customize is its own top-level link. This makes it clear which context you are about to enter.

fixes #32924. see #32678.

[jb510]

For the record this is now by FAR my favorite feature in 4.3. Seriously I'm tempted to update my client installs to trunk just to finally have this hourly nuisance fixed. Thank you... a million times... thank you.