[FrameSvg] Cache shadow margins and honor prefixes

Files I used for testing:

testframe.qml

Different margins for different prefix:

Svgs to update:

• widgets/background
• widgets/translucentbackground
• widgets/tooltip
• translucent/widgets/tooltip
• dialogs/background
• translucent/dialogs/background
• widgets/panel-background
• translucent/widgets/panel-background
• w̶i̶d̶g̶e̶t̶s̶/̶b̶u̶t̶t̶o̶n̶