faces: Port Load Preset dialog in ConfigAppearance to Kirigami.Dialog

Arjen Hiemstrarequested to merge
work/ahiemstra/appearancedialog into master
  • faces: Port Load Preset dialog in ConfigAppearance to Kirigami.Dialog

OverlaySheet doesn't work all that well here, using Kirigami.Dialog works better with regards to modality and placement. As a bonus it handles key events properly.

BUG: 491297

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