Feat #734 added the possibility to drag a subscribed parameter into the dashboard

[rdevoogtatstariongroup]

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Description

Feat #734
Dragging a subscribed parameter puts a ParameterSubscription on the drag payload. The dashboard's DragOver/Drop only matched Parameter/ParameterOverride, so the drop was rejected.

• Added GetParameterOrOverrideBase returns the payload itself for a ParameterOrOverrideBase, or parameterSubscription.Container as ParameterOrOverrideBase for a ParameterSubscription.
• DragOver / Drop now resolve via that helper and branch on the resolved Parameter/ParameterOverride type. Drop also folds the iteration check into the early-return guard.