Reported by @riandague:
This same issue has occurred in the past and was fixed.
https://www.genuitec.com/forums/topic/expandable-tree-view-icon-alignment-at-high-dpi/
It is now occurring in Photon. I do not have this issue in Oxygen.
Eclipse IDE for C/C++ Developers
Version: Photon Release Candidate 1 (4.8.0RC1)
Build id: 20180524-1423
Windows 10 1803
200% DPI Scaling