RFT Plot: Ensemble curve set selection and highlighting

[magnesj]

Summary

Improve the RFT plot UX when multiple ensemble curve sets are displayed:

1. Legend item ordering — Legend items in the plot now follow the same order as in the project tree (m_ensembleCurveSets index order), instead of being sorted by pointer address.

2. Project tree selection → plot highlight — When a RimWellRftEnsembleCurveSet is selected in the project tree, the plot responds by reducing opacity for member curves of all other curve sets. Statistics curves (ENSEMBLE_RFT) are unaffected and remain visible. The plot reverts to normal when selection is cleared.

3. Legend click → project tree selection — Clicking a legend item in the RFT plot selects the corresponding ensemble curve set in the project tree, enabling two-way navigation between the plot and the tree.

4. Missing update of new RFT curve sets — Make sure RFT curves from an newly imported ensemble is displayed correctly.

Implementation notes

• RimWellRftPlot now inherits caf::SelectionChangedReceiver to react to project tree selection changes.
• A QMetaObject::Connection is stored and explicitly disconnected in deleteViewWidget() to prevent use-after-free. The lambda capturing this is additionally guarded with a caf::PdmPointer.
• Legend ordering uses a custom std::set comparator based on m_ensembleCurveSets.indexOf().