Porting to KSvg

For Plasma 6, we're porting all instances of PlasmaCore.Svg, PlasmaCore.SvgItem, and PlasmaCore.FrameSvgItem to their new drop-in replacements here in the KSVG repo. The classes in plasma-framework have been removed in https://invent.kde.org/frameworks/plasma-framework/-/merge_requests/852 and https://invent.kde.org/frameworks/plasma-framework/-/merge_requests/879.

Relevant Merge Requests to port to KSvg:

• https://invent.kde.org/frameworks/plasma-framework/-/merge_requests/787
• plasma/plasma-workspace!2959 (merged)
• plasma/plasma-workspace!3190 (merged)
• plasma/plasma-desktop!1531 (merged)
• plasma/kdeplasma-addons!391 (merged)
• plasma/plasma-sdk!86 (merged)
• plasma/kwin!4175 (merged)
• plasma/kwin!4342 (merged)
• plasma/kwin!4345 (merged)
• plasma/kscreenlocker!151 (merged)
• plasma/kscreen!222 (merged)
• plasma/plasma-nm!255 (merged)
• plasma/plasma-pa!185 (merged)
• plasma/bluedevil!131 (merged)
• plasma/plasma-nano!43 (merged)
• plasma/plasma-welcome!85 (merged)
• documentation/develop-kde-org!296 (merged)
• libraries/kirigami-addons!108 (merged)

Getting it through kdereview: #2