Inconsistent output rounding for layer shell surfaces

[nebneb0703]

Outputs will ceil when applying fractional scaling to the dimensions:

smithay/src/desktop/space/mod.rs

Line 302 in 0c2230f

.to_i32_ceil(),

However when arranging layer shell surfaces, the output geometry is rounded:

smithay/src/desktop/wayland/layer.rs

Line 262 in 0c2230f

.to_i32_round();

This can lead to off-by-one errors in layer shell surface positioning with fractional scaling, meaning that surfaces anchored to a right or bottom edge may have a 1px gap between the surface (input region) and the actual edge of the output.