Allow passing custom axis tick formatters to VisCanvas

[axelboc]

Fix #1701

VisCanvas' internal tick formatter is meant as a good default:

• It uses D3 with format .3~g to strongly limit the number of characters and prevent tick labels from overflowing.
• It tells D3 to force exponent notation for numbers such as 0.00000123 (for which D3 doesn't respect the precision in g mode).
• It skips rendering some tick labels in log scale when space is limited.

Unfortunately, this is far from perfect.

Finding the perfect tick formatting algorithm is just not possible, so the idea with this PR is to allow consumers of VisCanvas to implement one that works for their use case.

I think this opens the door to a lot of use cases. For instance, in the new VisCanvas story that demonstrates the use of formatTick, I pass a formatter that uses toFixed for decimal numbers, and toString for integers.

One could even imagine toggling between different tick formatters based on zoom level using a combination of useCameraState and an external store (since useCameraState can only be used inside VisCanvas).