Portal/AGO: Display field descriptions on layer data page

[JoshKalov]

Portal and ArcGIS Online can store full metadata information for a layer. This includes field metadata like field descriptions. As a user, finding the field descriptions on a Portal/AGO layer requires clicking on Metadata and then navigating a confusing mess of metadata tabs and subtabs to find field descriptions.

Meanwhile, Portal/AGO users can click on the "Data" and then "Fields" buttons on the layer page to quickly access a basic list of field names and field types.

These data field information pages should include the field description information from the metadata so that users can quickly see and understand fields without needing to dig into complex layer metadata.