Math/Screen: fix coding style
Math/Screen: remove useless optimized scale==100 special case

Integer multiplication is fast enough.  May be as fast as the
"if/else".
Math/Screen: remove ineffective sin/cos cache

Angle::ifastsine() and Angle::ifastcosine() are just a simple table
lookup.  Tests have shown that PolygonRotateShift()'s cache hits
rarely anyway.

This makes PolygonRotateShift() thread-safe.
Math/Screen: remove useless Angle::AsBearing() call
Math/Screen: pass RasterPoint to PolygonRotateShift()
Screen/Layout: add unsigned Scale() overloads
Math/Screen: use Layout::FastScale()

Eliminate duplicate code.