Track palette opacity through the renderer

The depth buffer allows us to render fully opaque objects in any order without changing the final result (ignoring z-fighting). The next step of the renderer depth-buffer rewrite is to take advantage of this fact to reorder rendering by type (to reduce batch breakage) instead of by screen position.

1. Add an Opaque (or maybe Translucent) flag to the IPalette interface
2. Add an Opaque (or maybe Translucent) flag to the IRenderable interface, which in most implementations will return the value from the renderable's palette.
3. Adjust the TS mod rules to provide opaque (with legacy shadow-index remapping disabled) and non-opaque versions of palettes as needed.

Most (but IIRC not all) TS artwork splits shadows into their own frames, so most of the main artwork can use opaque palettes. The stealth effect currently works by swapping palettes, so we do not need to do any additional work to support that.

Start by locating the IPalette and IRenderable interfaces, their implementations, and the TS mod rules. Trace how palettes and renderables are passed through the renderer, then verify that opaque and non-opaque variants support the intended ordering and shadow-index behavior.