RectShape: add control over where the stoke goes (#5647)

Adds `RectShape::stroke_kind` so you can select if the stroke goes
inside, outside, or is centered on the rectangle.

Also adds `RectShape::round_to_pixels` so you can override
`TessellationOptions::round_rects_to_pixels`.

crates/epaint/src/shape_transform.rs

@@ -63,6 +63,8 @@ pub fn adjust_colors(
             rounding: _,
             fill,
             stroke,
+            stroke_kind: _,
+            round_to_pixels: _,
             blur_width: _,
             brush: _,
         }) => {