containments/panel: add icon applet to the left of the first task/window manager

Fushan Wenrequested to merge
work/fuf/panel/BUG454105-drop-icon-hack into master

Find any applet with "task" or "window" in their pluginName, and insert application icon applets to the left of it.

BUG: 454581 FIXED-IN: 5.25 CCBUG: 454105

Edited by Fushan Wen

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