Fix java shadow biases + minor cleanups

- constant bias and normal bias default values in java didn't match
  C++ or the documentation

- stable shadows were enabled by default in java

- polygon offset biases were missing from the java API

- document and don't apply polygon offset to VSM

- remove unused code

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

@@ -76,7 +76,9 @@ extern "C" JNIEXPORT void JNICALL
 Java_com_google_android_filament_LightManager_nBuilderShadowOptions(JNIEnv* env, jclass,
         jlong nativeBuilder, jint mapSize, jint cascades, jfloatArray splitPositions,
         jfloat constantBias, jfloat normalBias, jfloat shadowFar, jfloat shadowNearHint,
-        jfloat shadowFarHint, jboolean stable, jboolean screenSpaceContactShadows, jint stepCount,
+        jfloat shadowFarHint, jboolean stable,
+        jfloat polygonOffsetConstant, jfloat polygonOffsetSlope,
+        jboolean screenSpaceContactShadows, jint stepCount,
         jfloat maxShadowDistance, jint vsmMsaaSamples, jfloat blurWidth) {
     LightManager::Builder *builder = (LightManager::Builder *) nativeBuilder;
     LightManager::ShadowOptions shadowOptions {
@@ -88,6 +90,8 @@ Java_com_google_android_filament_LightManager_nBuilderShadowOptions(JNIEnv* env,
             .shadowNearHint = shadowNearHint,
             .shadowFarHint = shadowFarHint,
             .stable = (bool)stable,
+            .polygonOffsetConstant = polygonOffsetConstant,
+            .polygonOffsetSlope = polygonOffsetConstant,
             .screenSpaceContactShadows = (bool)screenSpaceContactShadows,
             .stepCount = uint8_t(stepCount),
             .maxShadowDistance = maxShadowDistance,