Add topBarElevationShadowEnabled style property (#579)

related to #557 #474 #125

android/app/src/main/java/com/reactnativenavigation/params/StyleParams.java

     public Color topBarColor;
     public CollapsingTopBarParams collapsingTopBarParams;
     public boolean topBarHidden;
+    public boolean topBarElevationShadowEnabled;
     public boolean topTabsHidden;
     public boolean drawScreenBelowTopBar;
 

android/app/src/main/java/com/reactnativenavigation/params/parsers/StyleParamsParser.java

         result.collapsingTopBarParams = new CollapsingTopBarParamsParser(params).parse();
         result.titleBarHidden = getBoolean("titleBarHidden", getDefaultTopBarHidden());
         result.topBarTransparent = getBoolean("topBarTransparent", getDefaultTopBarHidden());
+        result.topBarElevationShadowEnabled = getBoolean("topBarElevationShadowEnabled", getDefaultTopBarElevationShadowEnabled());
         result.titleBarTitleColor = getColor("titleBarTitleColor", getDefaultTitleBarColor());
         result.topBarTranslucent = getBoolean("topBarTranslucent", getDefaultTopBarTranslucent());
         result.titleBarHideOnScroll = getBoolean("titleBarHideOnScroll", getDefaultTitleBarHideOnScroll());
         return AppStyle.appStyle != null && AppStyle.appStyle.topBarTransparent;
     }
 
+    private boolean getDefaultTopBarElevationShadowEnabled() {
+        return AppStyle.appStyle == null || AppStyle.appStyle.topBarElevationShadowEnabled;
+    }
+
     private boolean getDefaultTopBarTranslucent() {
         return AppStyle.appStyle != null && AppStyle.appStyle.topBarTranslucent;
     }

android/app/src/main/java/com/reactnativenavigation/views/TopBar.java

         setVisibility(styleParams.topBarHidden ? GONE : VISIBLE);
         titleBar.setStyle(styleParams);
         setTopTabsStyle(styleParams);
+        if (!styleParams.topBarElevationShadowEnabled) {
+            disableElevationShadow();
+        }
     }
 
     private void setTransparent() {
         setBackgroundColor(Color.TRANSPARENT);
+        disableElevationShadow();
+    }
+
+    private void disableElevationShadow() {
         if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
             setOutlineProvider(null);
         }

src/deprecated/platformSpecificDeprecated.android.js

     topBarColor: processColor(originalStyleObject.navBarBackgroundColor),
     topBarTransparent: originalStyleObject.navBarTransparent,
     topBarTranslucent: originalStyleObject.navBarTranslucent,
+    topBarElevationShadowEnabled: originalStyleObject.topBarElevationShadowEnabled,
     collapsingToolBarImage: originalStyleObject.collapsingToolBarImage,
     collapsingToolBarCollapsedColor: processColor(originalStyleObject.collapsingToolBarCollapsedColor),
     titleBarHidden: originalStyleObject.navBarHidden,