Need to allow users to edit a value while constraining it via tooltip menu items

[franknoirot]

Users can "constrain" values like the length or angle of a line, or the radius of a circle, by making them named values. This is available when the user hovers over a segment, as an "overlay menu" button for each constrainable value. However, the modal that appears then provides no way to review or edit the value, only the ability to provide a name.

This modal should allow the user to review and edit the value, and optionally "constrain" it by giving it a name, doing math, or invoking a function within.