Raise unit test coverage from 49% to 81%

[afarber]

Unit test coverage was at 49% of instructions (38% of branches), and the gate only required 20%. Several public classes had no tests at all: Circle, GroundOverlay, TileOverlay, every *Options builder, PredefinedTileProviders and the Projection class.

What's in here:

• New tests for those classes, plus MapControllerOverlaysTest, which covers circles, ground and tile overlays, their touch handling, info window hits, and one draw() call with every shape type (holes, geodesic, dash patterns, style spans, rotated ground overlays, tile overlays above and below the base map)
• Removed five private draw helpers in MapController (drawPolylines, drawPolylineWithSpans, drawPolygons, drawCircles, drawMarkers). Nothing called them; draw() uses the zIndex-aware versions. That's about 250 lines of dead code
• Coverage gate raised from 20% to 75%
• The test table in TESTING_UNIT.md was quite out of date, so it's regenerated with the real counts (456 tests in 35 classes)

Result: 81% instructions, 79% lines, 65% branches. The biggest remaining gap is OpenMapView itself (23%), mostly touch handling, which the instrumented tests exercise on a device instead.

Merges cleanly with #48, which touches the same script.