CallStyle: Load conversation icon in setDataAsync

Loading ConversationIcon Drawable on the main thread causes ANR. This CL offloads this process on the background thread when call_style_async_set_data is enabled.

Bug: 293961072
Test: presubmit
Flag: ACONFIG android.widget.flags.call_style_async_set_data DEVELOPMENT
Change-Id: If44563698e83eab7cabf83d95b845047edb70ba9