Use Axes instead of axes in galleries

[timhoffm]

Part of #18726.

On a side-note: What I have learned from this: Even when knowing the definitions and differences between Axes and axes as a simple plural of axis, it is quite challenging to sort out which one to use in a couple of places. I have now a vague impression how confusing that naming may be to our users.

[story645]

and axes as a simple plural of axis,

If we still do this anywhere, we should probably change it to x and y (and/or whatever else) axis to save everyone some trouble.

[timhoffm]

If we still do this anywhere, we should probably change it to x and y (and/or whatever else) axis to save everyone some trouble.

Possibly in some places, though that's not practical everywhere. There are edge cases like axes coordinates that I have not touched and others cases where additional qualification is not needed or rather distracting when the context is clear. One could grep through the remaining "axes", but overall I think that's a second-order improvement. Consistently using Axes where it clearly denotes the object and is not a multiple of axis (=this PR) is the main improvement to reduce confusion.

[ksunden]

Similar to #27105, a couple notes here and there, but largely agree.

I so still have the figure or Axes feels incongruent when in close proximity and exactly one of them is capitalized, though that seemed less common as I read through this set of files.