Colorbar: Support customize tick label style

[Maoyao233]

New Contributors:
Please review CONTRIBUTING.md

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Purpose:
In Colorbar, the color of the tick labels is always black, which makes it hard to be seen in dark themes. This PR adds a new TickLabelStyle function to ColorBar, so that the style can be customized.

[bclehmann]

I think we could probably improve this by having this be automatically updated when the style changes. So that the colour of the Colorbar ticks is the same as the axis ticks.

[swharden]

I think we could probably improve this by having this be automatically updated when the style changes. So that the colour of the Colorbar ticks is the same as the axis ticks.

For now it seems okay to leave it exposed to let the user have full control over it. I also exposed fields for customizing the tick mark length, width, and color (independent of the label color). Thanks for this PR @Maoyao233, and @bclehmann for your review!