Fix unreadable dev menu header on dark theme apps (facebook#37253)

Summary:
Pull Request resolved: facebook#37253

Currently the Dev Menu has unreadable header/subtitle on apps with Dark theme. Here I'm fixing it:
* First I'm adding support for Dark Theme to RN Tester (we were forcign ligth theme).
* Then I'm removing any color reference and defaulting to the theme provided colors.

Changelog:
[Android] [Fixed] - Fix unreadable dev menu header on dark theme apps

Reviewed By: mdvacca

Differential Revision: D45566321

fbshipit-source-id: 947693aefdea846fec927a2cfa4d8236e02e0bfd

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/devsupport/DevSupportManagerBase.java

@@ -17,7 +17,6 @@
 import android.content.IntentFilter;
 import android.content.pm.PackageInfo;
 import android.content.pm.PackageManager;
-import android.graphics.Color;
 import android.graphics.Typeface;
 import android.hardware.SensorManager;
 import android.util.Pair;
@@ -498,23 +497,21 @@ public void onOptionSelected() {
       return;
     }
 
-    final LinearLayout header = new LinearLayout(getApplicationContext());
+    final LinearLayout header = new LinearLayout(context);
     header.setOrientation(LinearLayout.VERTICAL);
 
-    final TextView title = new TextView(getApplicationContext());
+    final TextView title = new TextView(context);
     title.setText(context.getString(R.string.catalyst_dev_menu_header, getUniqueTag()));
     title.setPadding(0, 50, 0, 0);
     title.setGravity(Gravity.CENTER);
-    title.setTextColor(Color.DKGRAY);
     title.setTextSize(16);
     title.setTypeface(title.getTypeface(), Typeface.BOLD);
 
-    final TextView jsExecutorLabel = new TextView(getApplicationContext());
+    final TextView jsExecutorLabel = new TextView(context);
     jsExecutorLabel.setText(
         context.getString(R.string.catalyst_dev_menu_sub_header, getJSExecutorDescription()));
     jsExecutorLabel.setPadding(0, 20, 0, 0);
     jsExecutorLabel.setGravity(Gravity.CENTER);
-    jsExecutorLabel.setTextColor(Color.GRAY);
     jsExecutorLabel.setTextSize(14);
 
     header.addView(title);

packages/rn-tester/android/app/src/main/res/values/styles.xml

@@ -1,9 +1,8 @@
 <resources>
 
     <!-- Base application theme. -->
-    <style name="AppTheme" parent="Theme.AppCompat.Light.NoActionBar">
+    <style name="AppTheme" parent="Theme.AppCompat.DayNight.NoActionBar">
         <!-- Customize your theme here. -->
-        <item name="android:textColor">#000000</item>
         <item name="android:editTextBackground">@drawable/rn_edit_text_material</item>
     </style>