Fixes#13479
This also fixes the gaps you can sometimes observe in outlines
(screenshot from main, not this PR):
<img width="636" alt="outline-gaps"
src="https://github.com/user-attachments/assets/c11dae24-20f5-4aea-8ffc-1894ad2a2b79">
The outline around the last item in each section has vertical gaps.
Draw the outlines with corner radius using the existing border rendering
for uinodes. The outline radius is very simple to calculate. We just
take the computed border radius of the node, and if it's greater than
zero, add it to the distance from the edge of the node to the outer edge
of the node's outline.
---
<img width="634" alt="outlines-radius"
src="https://github.com/user-attachments/assets/1ecda26c-65c5-41ef-87e4-5d9171ddc3ae">
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Co-authored-by: Jan Hohenheim <jan@hohenheim.ch>
cd9fec3547