Proposal: DragStarting with right mouse button

# Proposal: DragStarting event raised/enabled with right mouse button

## Summary

We would like to implement a right drag -> drop -> open context menu behavior in our application. Currently the DragStarting event is only fired when using the left mouse button. We propose enabling the event to be fired even when using the right mouse button.

## Rationale

* Drag with right mouse button -> Drop -> Context menu is a standard windows behavior.

## Scope

## Important Notes

## Open Questions

Start with docs/feature_proposal_process.md and review how the existing DragStarting event behaves. The proposal does not name implementation files or tests; done would require agreement on right-button drag behavior, the API change, and corresponding validation.

Written by the indexing model from the issue text.