Global region in the "Review changes" panel is overly verbose

This MR just implements the most trivial fix, and that is changing the label in PageRegion. But, this also affects the label everywhere, and that might not be desirable? In that case, maybe we should add a dedicated getAutoSaveLabel() method on entities instead?

This definitely is not a bug. It works exactly as intended.

#4: that's exactly why I named it this way, actually! 😄 Plus, it matched the label of the page template prior to #3501600: Split 1 PageTemplate config entity into N PageRegion config entities — which also included the theme name.

But @lauriii beat me to it:

since it's only possible to modify and review regions for the default theme.

Agreed. There's no potential for confusion.

I'll fix the last failing test and get this in.