Include editable locations in JSON output of list

This matches the JSON format with the default columns format.

Author: uranusjr

news/7764.feature

@@ -0,0 +1,3 @@
+Include ``location`` field for editable distribution entries in
+``pip list --json``, so the fields outputted match the default "columns"
+format.

src/pip/_internal/commands/list.py

@@ -303,8 +303,9 @@ def format_for_json(packages, options):
             'name': dist.project_name,
             'version': six.text_type(dist.version),
         }
-        if options.verbose >= 1:
+        if options.verbose >= 1 or dist_is_editable(dist):
             info['location'] = dist.location
+        if options.verbose >= 1:
             info['installer'] = get_installer(dist)
         if options.outdated:
             info['latest_version'] = six.text_type(dist.latest_version)