[MaterialAutoCompleteTextView] Default item layout not available with ExposedDropdownMenu for ArrayAdapters

Is your feature request related to a problem? Please describe.

When we set the items of MaterialAutoCompleteTextView on the XML with

     <com.google.android.material.textfield.MaterialAutoCompleteTextView
         app:simpleItems="@array/customer_types"

We can see a color change of the selected item when the dropdown menu is shown.

If we set the items with an ArrayAdapter as

    val customerTypes = resources.getStringArray(R.array.customer_types)
    val adapter = ArrayAdapter(this, android.R.layout.simple_spinner_dropdown_item, customerTypes)
    arrayAdapter.setAdapter(adapter)

The coloring of the selected item is not working. I've tried many available item layouts and none worked as the default. I looked at the code and I saw these lines

    simpleItemLayout =
        attributes.getResourceId(
            R.styleable.MaterialAutoCompleteTextView_simpleItemLayout,
            R.layout.mtrl_auto_complete_simple_item);

As far as I can see this is not available to use.

Describe the solution you'd like

Able to give the layout to an ArrayAdapter so that the selected item can be colored ( there is already XML for the color of the selected simpleItemSelectedColor)

Describe alternatives you've considered

I've tried to create my item layouts, however, I couldn't see any of the state_??? are helpful for the background drawable. Is it possible to write this behavior?

Start in MaterialAutoCompleteTextView.java around the simpleItemLayout resource lookup and compare the XML simpleItems path with ArrayAdapter usage. Investigate how simpleItemSelectedColor is applied and determine how an ArrayAdapter can receive the default item layout; done means the selected item is colored for ArrayAdapters as it is for simpleItems.