Fix filament colors in Hotends Info

[BenJule]

Summary

• color the hotend images in the Hotends Info view using each hotend's filament color
• color the enlarged hover preview as well
• preserve the filament color after DPI rescaling
• refresh the displayed color when it changes without a nozzle status change
• reuse the existing nozzle bitmap coloring helper

Testing

• ran git diff --check
• ran targeted C++ syntax checks for:
  • wgtDeviceNozzleRack.cpp
  • wgtDeviceNozzleRackUpdate.cpp
• both targeted syntax checks completed successfully
• no local full build was performed

Fixes #9576