Port back to KFilePlacesView

This removes the custom-view engine version of the places panel and replaces it with the upstream KFilePlacesView from KIO.

---

Depends on frameworks/kio!670 (merged)

Left is old, Right is new:

I have ported all features I could think of:

• "New tab" an "New window" in context menu, works also for when a drive is not mounted yet, opens once mounting has completed
• Middle click or Ctrl+click to open a place in a new tab
• "Unlock panels", "Configure trash" in context menu
• Places icon size setting is carried over to the new view, saves and restores fine, both fixed and the weird "dynamic" size mode
• Trash icon reflecting trash full/empty
• Adding, editing, removing, hiding places works
• show all places works, also from "Sidebars" menu
• Dragging a file or folder over a place and waiting, switches folders when this is enabled in settings
• Unmounted a drive whilst the terminal panel was on it, correctly cd $HOME and then carried on unmounting

There are a few quirks but now that we have a single view again and given the time till Gears 22.04 comes out, we'll have some time to address them:

• The animation when items resize, come, and go are laggy
• Wrong high-dpi pixmap chosen during resize
• Overlay painter (e.g. unmounted USB drive) uses wrong high-dpi pixmap
• Spacing/sizing/padding is slightly different
• Free space bar is too narrow with Breeze style, also only shows on hover
• Dragging a folder ontop of a place always adds it to the panel even if you actually wanted to move/copy/link it into the folder; dragging a file works fine, though

But please let's not get let down by those quirks, it's 4000 lines of code removed (almost 10% of Dolphin's code base!) and once we have the views unified, we can finally start thinking about adding new features we've wanted fr the longest time, such as an inline "eject" button…

@dfaure @ahmadsamir @meven @nicolasfella @alex @elvisangelaccio