feat: 增加设置任务栏是否开启窗口多开的接口

增加接口setShowMultiWindow和showMultiWindow接口，用于设置和返回任务栏是否支持窗口多开的功能

Log: 增加设置任务栏是否开启窗口多开的功能
Influence: 控制中心-个性化-任务栏，设置开启或者关闭任务栏支持窗口多开，观察任务栏相同的应用打开多个窗口的情况下，是否在多开区域存在多开的窗口
Task: https://pms.uniontech.com/task-view-170977.html
Change-Id: I208aba19f3ab94a02f72e64d0d4eeb1e83a7a6bf

misc/dconf/com.deepin.dde.dock.json

@@ -161,6 +161,16 @@
 			"description": "show or hide recent app in dock",
 			"permissions": "readwrite",
 			"visibility": "private"
+		},
+		"Show_MultiWindow": {
+			"value": false,
+			"serial": 0,
+			"flags": [],
+			"name": "Show_MultiWindow",
+			"name[zh_CN]": "*****",
+			"description": "show or hide Multi Window in dock when the Entry has subWindow",
+			"permissions": "readwrite",
+			"visibility": "private"
 		}
 	}
 }