applets/kicker: set mirroring for submenu opening explicitly

Christoph Wolkrequested to merge
cwo/plasma-workspace:kicker_dialog_mirrored into master

Reason for the change

Kicker's submenu placement is based on the system's layout direction. This mostly works, but breaks for far-edge panels (right side in ltr, left side in rtl), where Kicker (partially) flips its orientation. This isn't a huge problem for submenus (which have their position forced by the screen edge anyway), but sub-submenus open in the wrong direction, covering Kicker's (main) menu.

Instead, we make the direction where dialogs should be placed an explicit property of the SubMenu class, so we can set it from the qml side.

Test plan

Not independently testable, without changes in p-d everything should work as usual

Screenshots or screen recordings

N/A

Bugs fixed

N/A

patch for p-d in a bit

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