Add SpaEnvironmentFactory

To support different config for different Settings App.
Set SpaEnvironment instance in application.onCreate
Get SpaEnvironment instance from SpaEnvironmentFactory, rather than pass through parameter.

Bug: 244122804
Test: manual - build Gallery & Settings
Change-Id: I15600a085c1b7c63d37399e85aa8c71659cccc4e
diff --git a/packages/SettingsLib/Spa/gallery/AndroidManifest.xml b/packages/SettingsLib/Spa/gallery/AndroidManifest.xml
index e583138..0a4972f 100644
--- a/packages/SettingsLib/Spa/gallery/AndroidManifest.xml
+++ b/packages/SettingsLib/Spa/gallery/AndroidManifest.xml
@@ -18,12 +18,13 @@
     package="com.android.settingslib.spa.gallery">
 
     <application
+        android:name=".GalleryApplication"
         android:icon="@mipmap/ic_launcher"
         android:label="@string/app_label"
         android:supportsRtl="true"
         android:enableOnBackInvokedCallback="true">
         <activity
-            android:name=".MainActivity"
+            android:name=".GalleryMainActivity"
             android:exported="true">
             <intent-filter>
                 <action android:name="android.intent.action.MAIN" />