fix(settings): hand focus back to the page when a picker closes

[fengqiu233]

Summary

• give the language and typeface pickers the settings page focus handle back when they close, so an action raised by a later click still finds a dispatch path
• take that handle in SearchPopup::new rather than through a setter, so no caller can forget it

Closes #584

[fengqiu233]

Hi, I found a new bug. It's still the same issue:

• In the first step, switching the language doesn't actually switch it.

• After clicking Search and other areas outside, the fullscreen button doesn't respond.

• The fullscreen button only responds after I click another area.

So far, I have only fixed the issue where selecting from the menu bar and then clicking the fullscreen button allows me to enter fullscreen mode.：(

Asking you to fix the bug.

[fengqiu233]

It's already fixed, please merge it

Fixes: #584