Dynamically Display Projection Units in Buffer Distance Field

[arjxn-py]

The buffer distance unit depends on the selected projection.
Maybe Use proj4js to determine the projection unit dynamically:

import proj4 from "proj4";
const unit = proj4("EPSG:4326").oProj.units; // Example output: "degrees"

Originally suggested by @mfisher87 in #529 (comment)