SSCT optimizations and fixes

- Use lower depth LOD as the cone radius increases.
  This is the same technique we use for SAO.
  The better cache access significantly improve performance.
  On a test on Pixel4 at 585MHz, SAO pass improves by 30%.
  This also helps the algorithm scale with the shadow distance.

- Shadow direction/length no longer dependent on aspect-ratio and camera
  orientation.
  This is fixed by doing all the computations in screen-space instead of 
  normalized screen space.

- Shadow parameters are no longer dependent on the field of view.

- Also rename dominantLightShadowing.fs to ssct.fs

- remove zoom parameter, it wasn't very useful.

android/filament-android/src/main/cpp/View.cpp

@@ -217,7 +217,7 @@ extern "C" JNIEXPORT void JNICALL
 Java_com_google_android_filament_View_nSetSSCTOptions(JNIEnv *, jclass, jlong nativeView,
         jfloat ssctLightConeRad, jfloat ssctStartTraceDistance, jfloat ssctContactDistanceMax,
         jfloat ssctIntensity, jfloat ssctLightDirX, jfloat ssctLightDirY, jfloat ssctLightDirZ,
-        jfloat ssctDepthBias, jfloat ssctDepthSlopeBias, jfloat ssctScale, jint ssctSampleCount,
+        jfloat ssctDepthBias, jfloat ssctDepthSlopeBias, jint ssctSampleCount,
         jint ssctRayCount, jboolean ssctEnabled) {
     View* view = (View*) nativeView;
     View::AmbientOcclusionOptions options = view->getAmbientOcclusionOptions();
@@ -228,7 +228,6 @@ Java_com_google_android_filament_View_nSetSSCTOptions(JNIEnv *, jclass, jlong na
     options.ssct.lightDirection = math::float3{ ssctLightDirX, ssctLightDirY, ssctLightDirZ };
     options.ssct.depthBias = ssctDepthBias;
     options.ssct.depthSlopeBias = ssctDepthSlopeBias;
-    options.ssct.scale = ssctScale;
     options.ssct.sampleCount = (uint8_t)ssctSampleCount;
     options.ssct.rayCount = (uint8_t)ssctRayCount;
     options.ssct.enabled = (bool)ssctEnabled;