Move title panel to inside the center content area

[jasongrout]

References

Fixes issues brought up in #9105

#9274 is an alternative to this PR that preserves the existing title-at-the-top behavior.

After playing with both alternatives a bit, I like #9274 (combined with #9270) over this PR.

Code changes

User-facing changes

This prevents the menu from jumping up and down when toggling single-document mode. Also, it mirrors where the tabs are in normal mode, so it’s easy to see the correspondence between the tab title and the titlebar.

This is an experiment to see if it improves the UX overall, at least good enough to ship for 3.0. It also takes out some hacks we had with the icon to the left of the menu floating up above the bar it was on, etc.

Jumping from before (see #9105):

No jumping now:

Before

After

Backwards-incompatible changes

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[jasongrout]

Another approach is that we create a new single-document mode menu bar under the top bar. In single-document mode, we move the menu to the bar under the top area, and replace the menu with the title widget. That way the top bar stays on top, and only the menu moves, and you get the UX that we have now of the title at the very top. You still have a problem of menu jumping (if you switch the mode using the menu), but that's probably way less frustrating than the switch jumping.

[jtpio]

Nice, thanks!

It's possible this removes a bit of the "classic notebook look and feel" by moving the title down. But the fact that it fixes the jumping seems to outweigh it 👍

[jasongrout]

There is another alternative to the ux over at #9274

[jasongrout]

Closing in preference for #9274