Always include applicable fields in list --json

Since the JSON output is designed for machine consumption, it does not
make much sense to have the verbosity flag influence its output. This
change makes `installer` and `location` to always be included.

news/7764.feature

@@ -0,0 +1,2 @@
+Always include fields ``installer`` and ``location`` in ``pip list --json``
+output regardless of verbosity.

src/pip/_internal/commands/list.py

@@ -301,11 +301,10 @@ def format_for_json(packages, options):
     for dist in packages:
         info = {
             'name': dist.project_name,
+            'installer': get_installer(dist),
+            'location': dist.location,
             'version': six.text_type(dist.version),
         }
-        if options.verbose >= 1:
-            info['location'] = dist.location
-            info['installer'] = get_installer(dist)
         if options.outdated:
             info['latest_version'] = six.text_type(dist.latest_version)
             info['latest_filetype'] = dist.latest_filetype