Add property paths to "Fields" tab

Just noticed that, with the new fields UI and workflow, it's impossible to tell from the UI what property path was used for a certain field. With #2641390: Make field names and IDs editable, you could easily end up with two fields that look more or less identical, and have no way of telling them apart.

We should find some way to display the property path in that list – either as a separate column, or as a hover text, or something else.