Improve visibility of "minor" grid lines

[cihe13375]

Currently the "minor" grid lines are barely visible on a 4k monitor at normal distances:


It would be nice if they can be made more visible, e.g. by higher thickness or a brighter color.
It should be an option though imo, to avoid them being annoying when the grid is not used (or alternatively, add a way to hide the grid completely, like those purposed in #29713)

[peppy]

Right now, the line thickness is fixed regardless of display resolution. I think this is incorrect. It should have a minimum thickness, but get thicker when the resolution / DPI is high enough to warrant it.

#30072