[Feature] Highlight origin grid lines

[brenocq]

Discussed in #58

^{Originally posted by @dimateos January 14, 2025}

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In ImPlot, the grid lines all have the same color (both for minor and major ticks), except for the 2 lines passing by the origin, which have a brighter color for easy reference to the origin. In ImPlot3D, lines from major ticks stand out more than lines from minor ticks (which is good), but there is no special style for lines passing by the origin. Lines passing by the origin should stand out just like they do in ImPlot.

ImPlot

ImPlot3D