desktoptheme/breeze: put the background frame parts on whole pixels

The nine parts of widgets/background, and of its translucent variant, sat a fraction of a pixel off the grid, from editor noise: curls at the ends of the border paths, a gradient rect a fraction below the fill it edges, and group translations placing the parts at 30.9994 rather than 31.

A part a fraction taller than what it draws leaves its outermost pixels partly covered, so a border meant to be one shade along its whole length fell short of it at its two ends. Those ends are what changes on screen: up to 7 of 255 for a border on its own, at most 1 once composed as a frame.

Scale factors are untouched, since the parts are the right size once the rest is on the grid.

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This allows to remove ambiguities when caching the images into textures.

This is part of my effort to reduce VRAM usage of Plasma frameworks/ksvg!114