Fix outlines being offset diagonally by about half a pixel (#1668)

Fixes very subtle bug that caused outlines to be offset. With the gaps introduced in #1614 this became more quite apparent in some situations (at least if you're glued with your nose to the screen like myself ;))

crates/re_renderer/shader/composite.wgsl

@@ -20,7 +20,7 @@ var outline_voronoi_texture: texture_2d<f32>;
 @fragment
 fn main(in: FragmentInput) -> @location(0) Vec4 {
     let resolution = Vec2(textureDimensions(color_texture).xy);
-    let pixel_coordinates = resolution * in.texcoord;
+    let pixel_coordinates = floor(resolution * in.texcoord);
 
     // Note that we can't use a simple textureLoad using @builtin(position) here despite the lack of filtering.
     // The issue is that positions provided by @builtin(position) are not dependent on the set viewport,

crates/re_renderer/shader/outlines/jumpflooding_step.wgsl

@@ -20,7 +20,7 @@ var<uniform> uniforms: FrameUniformBuffer;
 fn main(in: FragmentInput) -> @location(0) Vec4 {
     let resolution = Vec2(textureDimensions(voronoi_texture).xy);
     let pixel_step = Vec2(f32(uniforms.step_width), f32(uniforms.step_width)) / resolution;
-    let pixel_coordinates = resolution * in.texcoord;
+    let pixel_coordinates = floor(resolution * in.texcoord);
 
     var closest_positions_a = Vec2(f32min);
     var closest_distance_sq_a = f32max;