fix: use proper dock DnD MIME data

[RigoLigoRLC]

对于将应用拖拽到Dock上固定的场景使用正确的MIME数据，并在不允许某应用固定到Dock上时不加入此MIME数据，以阻止Dock接受拖拽事件。此提交是占位包需求遗留问题的修复。

此PR目标为维护分支，与 linuxdeepin/dde-shell#818 互相依赖。

Log:
Bug: https://pms.uniontech.com/bug-view-279155.html

[deepin-ci-robot]

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[deepin-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: BLumia, RigoLigoRLC

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