pqTransferFunctionWidget: ensure interaction ends when color chooser dialog closes

When a node in the pqTransferFunctionWidget is double-clicked, a color chooser dialog appears to change the color. When the dialog is closed, if the mouse is moved over the transfer function widget right away, a "mouse button released" event can be lost, which results in the editor getting stuck in a mode where the node moves based on the movement of the mouse, resulting in an unintentional move of the node.

Fix this by creating a mouse button release event and sending it to the selected vtkControlPointsItem to let it know interaction is finished after the color editor dialog is closed.

Closes #20758 (closed)

Backport: release