As decided in D910, we use a new icon for incremental grid snapping and use its old one for absolute grid snapping.
This also touches the library_data_broken icon .dat files, seems some changes on its .svg entry landed in upstream without updating the other icon files (already noticed this when committing icon for auto-offset, but removed it from commit - leaving it in now to avoid further confusion)
Icon by @plyczkowski (made a tiny edit as it looked a bit blurry in 16x16). Thx!
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