ui: simplify draw_border

[deanlee]

Scissor mode is not required for border drawing and introduces unnecessary overhead.

@sshane : I haven’t found any case where scissor mode or double draw_rectangle_rounded_lines_ex calls are necessary.
Is there any specific reason we need to keep scissor mode for this case?

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[sshane]

There's a few pixels of camera view around the edges without the black. And then the scissor prevents overlap with sidebar

[deanlee]

ah got it — makes sense. It should be safe to remove the scissor now, since we already moved draw_border to run after rendering the camera view in PR #36348. there’s no visible camera view around the edges anymore, and the sidebar won’t overlap since the outer black border is now drawn using draw_rectangle_lines_ex. here’s the comparison with master:

Master	This Pr