Effect eyedroppers (other than keyers', which pick from the effect's
input) sample the composite the viewer shows; a test covers that on
main. But they, and the Info panel, read the shown frame as if it
covered the whole comp. With a Region of Interest, or the Extended
Viewer of a 3D view, the frame covers only that area, so they read a
pixel somewhere else. They now map the point through the area the
frame covers (`shown_region`, `frame_pixel`).
Tests: the_eyedropper_samples_under_the_pointer_in_a_region_of_interest
(ui_effect_controls), eyedropper_samples_straight_colour (fx_widgets).
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
