Fix: Modal dialogs don't have background color

Resolves #3129

apps/app/ui-tests-app/modal-view/login-page.xml

@@ -1,5 +1,5 @@
 <Page xmlns="http://schemas.nativescript.org/tns.xsd" shownModally="onShownModally" loaded="onLoaded" unloaded="onUnloaded" backgroundColor="Red">
-  <StackLayout backgroundColor="PaleGreen">
+  <StackLayout backgroundColor="PaleGreen" margin="10">
     <TextField hint="username" id="username" text="username"/>
     <TextField hint="password" id="password" text="password" secure="true"/>
     <Button text="Login" tap="onLoginButtonTap"/>

tns-core-modules/ui/page/page.android.ts

@@ -161,6 +161,7 @@ export class Page extends pageCommon.Page {
 
         this._onAttached(parent._context);
         this._isAddedToNativeVisualTree = true;
+        this._syncNativeProperties();
 
         ensureDialogFragmentClass();