Hide datastore from public api/add note on thread

Author: daymxn

firebase-common/src/main/java/com/google/firebase/datastore/DataStore.kt

@@ -23,6 +23,7 @@ import androidx.datastore.preferences.core.MutablePreferences
 import androidx.datastore.preferences.core.Preferences
 import androidx.datastore.preferences.core.edit
 import androidx.datastore.preferences.preferencesDataStore
+import com.google.firebase.annotations.concurrent.Background
 import kotlinx.coroutines.flow.firstOrNull
 import kotlinx.coroutines.runBlocking
 
@@ -33,6 +34,10 @@ import kotlinx.coroutines.runBlocking
  *
  * There should only ever be _one_ instance of this class per context and name variant.
  *
+ * Note that most of the methods in this class **block** on the _current_ thread, as to help keep
+ * parity with existing Java code. Typically, you'd want to dispatch this work to another thread
+ * like [@Background][Background].
+ *
  * > Do **NOT** use this _unless_ you're bridging Java code. If you're writing new code, or your
  * code is in Kotlin, then you should create your own singleton that uses [DataStore] directly.
  *
@@ -43,6 +48,8 @@ import kotlinx.coroutines.runBlocking
  *
  * @property context The [Context] that this data will be saved under.
  * @property name What the storage file should be named.
+ *
+ * @hide
  */
 class DataStorage(val context: Context, val name: String) {
   /**

firebase-common/src/main/java/com/google/firebase/datastore/package-info.java

@@ -0,0 +1,16 @@
+// Copyright 2023 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+/** @hide */
+package com.google.firebase.datastore;