Test layers on one engine and share selection and shader helpers

Layer display tests no longer re-check Cesium primitives in every layer:
they run on the fake engine, and one Cesium translation check per ground
kind lives in the Cesium engine's ground tests. Their harnesses are shared,
and the fake-engine, Cesium-engine and flights tests that repeated the
contract suite are gone, 340 tests in all.

The press-travel measurement is shared by the selection dispatcher and
CCTV, which loses its ScreenSpaceEventHandler shim and world-click module.
ALPR, installations and bikeshare share one selection keeper and selected
marker write. Layers with their own click rules keep their handlers.

Navara's pulse is a class like the ground pass, the ground and imagery
passes share the surface uniforms, and the colour, log-depth and occlusion
GLSL lives in one chunk module, each caller keeping its depth bias. The
ground suite runs inside the contract suite (--only=ground:), and fixture
and script names say what they test.

Behaviour is unchanged on both engines.

scripts/engine-coupling-baseline.json

@@ -7,10 +7,10 @@
     "navaraKindChecks": 1,
     "engineSniffCalls": 0,
     "engineExtensionReads": 3,
-    "groundEffectPasses": 1,
+    "groundEffectPasses": 0,
     "cesiumSdkLoads": 3,
-    "screenSpaceHandlerFiles": 4,
+    "screenSpaceHandlerFiles": 2,
     "engineNameLines": 27
   },
-  "measuredAt": "Drop leftover viewer paths"
+  "measuredAt": "One selection path and test level"
 }