[Expressive design] Add Slider's halo as a separate resource

<?xml version="1.0" encoding="utf-8"?>

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<selector xmlns:android="http://schemas.android.com/apk/res/android">

    <item android:color="@android:color/transparent" />

</selector>

 No newline at end of file

        <item name="thumbColor">@color/settingslib_expressive_color_slider_thumb</item>

        <item name="tickColorActive">@color/settingslib_expressive_color_slider_track_inactive</item>

        <item name="tickColorInactive">@color/settingslib_expressive_color_slider_track_active</item>

        <item name="haloColor">@android:color/transparent</item>

        <item name="haloColor">@color/settingslib_expressive_color_slider_halo</item>

    </style>

</resources>