dolphinmainwindow: switch to the new tab a context menu opens

Méven Carrequested to merge
work/meven/context-menu-activate-new-tab into master

Opening a folder in a new tab left that tab in the background whichever way it was asked for, so every "Open in New Tab" ended with a trip to the tab bar. A gesture which opens a tab now switches to it, and holding Shift down is what asks for a tab in the background. This covers the context menu entries, a middle click and a Ctrl+click on a folder, and the Folders panel.

The URL bar has always worked this way, where Alt+Return opens an active tab and Alt+Shift+Return a background one. Middle click and Ctrl+click had the two the other way round, so they are what changes direction here.

A selection of several folders still opens one tab each. The first of them is activated, and the tabs are created in the background first so that they keep the order of the selection.

Nothing told the user about the Shift key, so the entries which open a tab now carry a tooltip saying what it does, and their text becomes "Open in New Background Tab" while Shift is held down. That is what the delete entry already does between moving to the trash and deleting. Qt only shows tooltips in menus on request, and gives every entry its own text as one, so KToolTipHelper from KXmlGui is installed in main.cpp. It shows the tooltip of an entry only when it says more than the text of that entry. It also offers the "What's This" help of a widget on the line below its tooltip, which is new for Dolphin.

The Places panel and the breadcrumb live in KIO and follow in a separate merge request against frameworks/kio!2378. Neither merge request needs the other to land first, but it will be best to synchronize them so users have consistent behavior upon updating.

This is what https://bugs.kde.org/show_bug.cgi?id=388769 asks for. That report also carries the idea of a checkbox under Settings, Interface, Folders and Tabs to pick the default instead, so the bug is referenced rather than closed here. And https://discuss.kde.org/t/open-in-new-tab-should-immediately-switch-to-new-tab/49438

CCBUG: 388769

Edited by Méven Car

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