* Closes https://github.com/emilk/egui/issues/7647
This collects SnapshotResults within the Harness and adds a check to
enforce snapshot results are merged in case multiple Harnesses are
constructed within a test.
This should make snapshot updates via kitdiff/accept_snapshots.sh way
more useful since it should now always update all snapshots instead of
only the first one per test.
Selected text now gets the color of `visuals.selection.stroke.color`.
This means you can have inverted colors for selected text, like in the
new test:
<img width="154" height="46" alt="image"
src="https://github.com/user-attachments/assets/2666361d-d7e2-4d50-8e4d-2fcc128f1a81"
/>
It also means the color of selected text in labels matches that of the
text color of selected buttons.
