Fix: EEVEE: Imprecision in HiZ gather coordinates

The offset was only 0.5 which centered the gather
sample exactly on the first pixel of the quad.
With floating point arithmetic differences on Nvidia
this lead to the wrong set of texture pixel being
fetched by gather.

Using the coordinate at the center of the quad fixes
the issue.

Fix #123262

source/blender/draw/engines/eevee_next/shaders/eevee_hiz_update_comp.glsl

@@ -45,10 +45,10 @@ void main()
   /* Copy level 0. */
   ivec2 src_px = ivec2(kernel_origin + local_px) * 2;
 #ifdef HIZ_LAYER
-  vec2 samp_co = (vec2(src_px) + 0.5) / vec2(textureSize(depth_layered_tx, 0).xy);
+  vec2 samp_co = vec2(src_px + 1) / vec2(textureSize(depth_layered_tx, 0).xy);
   vec4 samp = textureGather(depth_layered_tx, vec3(samp_co, float(layer_id)));
 #else
-  vec2 samp_co = (vec2(src_px) + 0.5) / vec2(textureSize(depth_tx, 0));
+  vec2 samp_co = vec2(src_px + 1) / vec2(textureSize(depth_tx, 0));
   vec4 samp = textureGather(depth_tx, samp_co);
 #endif