[android] Modify Addon support

Bug 40011: Hide option for disallowing addons in private mode

Bug 40016: Allow inheriting from AddonCollectionProvider

This will allow implementing our own AddonsProvider in fenix.

mobile/android/android-components/components/feature/addons/src/main/java/mozilla/components/feature/addons/AddonManager.kt

@@ -494,6 +494,7 @@ class AddonManager(
         val installedAddon = Addon.newFromWebExtension(ext, installedState)
 
         addonUpdater.registerForFutureUpdates(installedAddon.id)
+        setAddonAllowedInPrivateBrowsing(installedAddon, true)
         completePendingAddonAction(pendingAction)
         onSuccess(installedAddon)
     }

mobile/android/android-components/components/feature/addons/src/main/java/mozilla/components/feature/addons/amo/AMOAddonsProvider.kt

@@ -63,7 +63,7 @@ internal const val PAGE_SIZE = 50
  * should remain valid before a refresh is attempted. Defaults to -1, meaning no cache
  * is being used by default
  */
-class AMOAddonsProvider(
+open class AMOAddonsProvider(
     private val context: Context,
     private val client: Client,
     private val serverURL: String = DEFAULT_SERVER_URL,
@@ -237,7 +237,7 @@ class AMOAddonsProvider(
     }
 
     @VisibleForTesting
-    internal fun writeToDiskCache(collectionResponse: String, language: String?) {
+    open fun writeToDiskCache(collectionResponse: String, language: String?) {
         synchronized(diskCacheLock) {
             getCacheFile(context, language, useFallbackFile = false).writeString { collectionResponse }
         }

mobile/android/android-components/components/feature/addons/src/main/res/layout/mozac_feature_addons_fragment_dialog_addon_installed.xml

@@ -53,6 +53,7 @@
         tools:text="@string/mozac_feature_addons_installed_dialog_description_2" />
 
     <androidx.appcompat.widget.AppCompatCheckBox
+        android:visibility="gone"
         android:id="@+id/allow_in_private_browsing"
         android:layout_width="wrap_content"
         android:layout_height="wrap_content"

mobile/android/android-components/samples/browser/src/main/res/layout/activity_installed_add_on_details.xml

@@ -70,6 +70,7 @@
                 app:drawableStartCompat="@drawable/mozac_ic_permissions" />
 
         <androidx.appcompat.widget.SwitchCompat
+            android:visibility="gone"
             android:id="@+id/allow_in_private_browsing_switch"
             android:layout_width="match_parent"
             android:layout_height="wrap_content"