[freezy]

Two new plain circle inserts and library fixes, authored with the in-library insert baking of freezy/VisualPinball.Engine#612.

Summary

• New inserts: plain 1in and 0.75in circles, each with its prefab, bake asset, normal and optical textures, the full set of colored materials (Amber, Blue, Clear, Green, Orange, Purple, Red, Teal, Yellow), a library database entry and thumbnails.
• Stale pre-bake materials: the 0.75in circle and 1.1875in triangle starburst inserts no longer keep the 1.1875in circle starburst's red material as the one they wore before their bake.
• Ray tracing: the 555 and 89 bulb lights are included in ray tracing, so ray-traced reflections see the lamps (see Reflect the playfield in the balls, light ray-traced reflections with every lamp, and toggle depth of field VisualPinball.Unity.Hdrp#38).
• The circle, rectangle and triangle insert prefabs lock proportional scaling on their root transforms, and the rectangle starburst materials serialize the default cavity color.