Merge the androidx into master.

Now Android Studio 3.2 and the androidx 1.0.0 versions are stable.
Merging the androidx features to the master is ready.

Author: thagikura

README.md

@@ -10,7 +10,7 @@ Add the following dependency to your `build.gradle` file:
 
 ```
 dependencies {
-    implementation 'com.google.android:flexbox:1.1.0-beta1'
+    implementation 'com.google.android:flexbox:1.1.0'
 }
 ```
 

build.gradle

@@ -22,7 +22,7 @@ buildscript {
         targetSdkVersion = 28
         compileSdkVersion = 28
 
-        androidGradlePluginVersion = "3.2.0-beta04"
+        androidGradlePluginVersion = "3.2.0"
         androidMavenGradlePluginVersion = "1.5"
         androidxCoreVersion = "1.0.0"
         androidxEspressoVersion = "3.1.0-alpha4"

demo-playground/src/main/res/menu/menu_main.xml

@@ -15,10 +15,11 @@ limitations under the License.
 -->
 <menu xmlns:android="http://schemas.android.com/apk/res/android"
     xmlns:tools="http://schemas.android.com/tools"
+    xmlns:app="http://schemas.android.com/apk/res-auto"
     tools:context="com.google.android.flexbox.MainActivity">
     <item
         android:id="@+id/action_settings"
         android:title="@string/action_settings"
         android:orderInCategory="100"
-        android:showAsAction="never" />
+        app:showAsAction="never" />
 </menu>

flexbox/src/androidTest/java/com/google/android/flexbox/test/TestViewHolder.kt

@@ -18,10 +18,11 @@ package com.google.android.flexbox.test
 
 import android.view.View
 import android.widget.TextView
+import androidx.recyclerview.widget.RecyclerView
 
 /**
  * ViewHolder implementation for a flex item for testing.
  */
-internal class TestViewHolder(itemView: View) : androidx.recyclerview.widget.RecyclerView.ViewHolder(itemView) {
+internal class TestViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {
     val textView: TextView = itemView.findViewById(R.id.textview)
 }

flexbox/src/main/java/com/google/android/flexbox/FlexboxLayoutManager.java

@@ -33,6 +33,7 @@
 import java.util.ArrayList;
 import java.util.List;
 
+import androidx.annotation.NonNull;
 import androidx.core.view.ViewCompat;
 import androidx.recyclerview.widget.LinearLayoutManager;
 import androidx.recyclerview.widget.LinearSmoothScroller;