Change SpaEnvironmentFactory interface.

Allow user reset the environment multiple times in tests.

Test: manual - build Gallery
Change-Id: I5279698034667cf870c22d2194bba16096c3c56f

packages/SettingsLib/Spa/gallery/src/com/android/settingslib/spa/gallery/GalleryApplication.kt

@@ -22,6 +22,6 @@ import com.android.settingslib.spa.framework.common.SpaEnvironmentFactory
 class GalleryApplication : Application() {
     override fun onCreate() {
         super.onCreate()
-        SpaEnvironmentFactory.instance = GallerySpaEnvironment
+        SpaEnvironmentFactory.reset(GallerySpaEnvironment)
     }
 }

packages/SettingsLib/Spa/spa/src/com/android/settingslib/spa/framework/common/SpaEnvironment.kt

@@ -24,19 +24,17 @@ private const val TAG = "SpaEnvironment"
 object SpaEnvironmentFactory {
     private var spaEnvironment: SpaEnvironment? = null
 
-    var instance: SpaEnvironment
+    fun reset(env: SpaEnvironment) {
+        spaEnvironment = env
+        Log.d(TAG, "reset")
+    }
+
+    val instance: SpaEnvironment
         get() {
             if (spaEnvironment == null)
                 throw UnsupportedOperationException("Spa environment is not set")
             return spaEnvironment!!
         }
-        set(env: SpaEnvironment) {
-            if (spaEnvironment != null) {
-                Log.w(TAG, "Spa environment is already set, ignore the latter one.")
-                return
-            }
-            spaEnvironment = env
-        }
 }
 
 abstract class SpaEnvironment {