代理设置组合框中文本大小未设置固定值，拉伸后大小发生变化

Log: 修复系统代理，网络，应用代理组合框布局问题
Bug: https://pms.uniontech.com/zentao/bug-view-50165.html
Change-Id: I775d1b8814cc6b96b437b961ed313aa037b89475
Reviewed-on: http://gerrit.uniontech.com/c/dde-control-center/+/6916
Reviewed-by: lvpeilong <lvpeilong@uniontech.com>
Reviewed-by: <mailman@uniontech.com>
Tested-by: <mailman@uniontech.com>