Improve placeholder text usability in Fabric

The current placeholder text in Fabric is causing inconvenience as it contains a valid value that users want to use directly. Users are forced to type out or copy/paste the placeholder value from another app. Work through all placeholders and ensure that wherever we use them, it's an actual accepted default value that makes sense for the user. Otherwise, remove it, and use a different UI concept like a dropdown, or a tooltip or hint or label next to the text field.