Allow to reuse existing search term

[glassez]

The search pattern text reflects that of the current search tab, unless it is manually edited.
The edited search pattern can be reset by double-clicking on one of the tabs.

The alternative option @bartonnen suggested is to simply follow the current tab regardless of whether the pattern has been edited or not. This behavior seems undesirable to me.

[thalieht]

Dunno if it's caused by this PR: Crash when dragging and dropping a tab outside the tab bar with the right click (can't reproduce with left)

1 SearchJobWidget::status   searchjobwidget.cpp 248 0x555555fc3f70 
2 SearchWidget::showTabMenu searchwidget.cpp    349 0x555555fd18e4 
3 SearchWidget::eventFilter searchwidget.cpp    189 0x555555fd017c 

[glassez]

Dunno if it's caused by this PR

Caused by #22122.
Should be fixed now.