Implement AAPT Bundle format

AAPT will scan XML files looking for the <aapt:attr> XML tag.

<!-- @layout/bundle.xml -->
<ImageView xmlns:aapt="http://schemas.android.com/aapt">
  <aapt:attr name="android:src">
    <vector android:pathData="..." ...>
    </vector>
  </aapt:attr>
</ImageView>

The SINGLE child element of the <aapt:attr> tag is extracted into its own top
level resource. It is given a generated name.

The parent element of <aapt:attr> is then given the resource attribute that was assigned
to the `name' attribute. The value is set to a reference to the generated resource.

<!-- @layout/bundle.xml -->
<ImageView android:src="@drawable/bundle_1.xml">
</ImageView>

<!-- @layout/bundle_1.xml -->
<vector android:pathData="..." ...>
</vector>

Bug:22627686
Change-Id: I8575fc4f739011402662fbf6b3db96df0012f598