ProjectExplorer: Re-do the EnvironmentWidget

Editing in the item view was cumbersome and did not generally allow one
variable to refer to another, as there was no defined order on the
assignments.
Therefore, we make the item view read-only and promote the batch editing
widget to be the standard input method. User changes are not sorted
anymore, except in the summary text of the details widget.

Fixes: QTCREATORBUG-28480
Change-Id: I225cf86fff7b001a57d663e1fd267a4645e695c4
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: hjk <hjk@qt.io>

src/plugins/projectexplorer/kitaspects.cpp

@@ -1480,8 +1480,7 @@ private:
         if (HostOsInfo::isWindowsHost())
             changes.removeAll(forceMSVCEnglishItem());
 
-        return sorted(std::move(changes), [](const EnvironmentItem &lhs, const EnvironmentItem &rhs)
-        { return QString::localeAwareCompare(lhs.name, rhs.name) < 0; });
+        return changes;
     }
 
     void initMSVCOutputSwitch(QVBoxLayout *layout)