Make all lines and rectangles crisp

[emilk]

• Merge this first: Round widget coordinates to even multiple of 1/32 #5517

This aligns all rectangles and (horizontal or vertical) line segments to the physical pixel grid in the epaint::Tessellator, making these shapes appear crisp everywhere.

• Closes Align shapes to physical pixel grid #5164
• Closes egui_demo_app color test lines #3667

This undoes a lot of the explicit, egui-side aligning added in:

• Fix blurry lines by aligning to pixel grid #4943

The new approach has several benefits over the old one:

• It is done automatically by epaint, so it is applied to everything (no longer opt-in)
• It is applied after any layer transforms (so it always works)
• It makes line segments crisper on high-DPI screens
• All filled rectangles now has sides that end on pixel boundaries

[github-actions]

Preview available at https://egui-pr-preview.github.io/pr/5518-emilkround-shapes-to-pixels
Note that it might take a couple seconds for the update to show up after the preview_build workflow has completed.