document that print(x) and repr(x) call 2-arg show (#53927)
As mentioned
[here](https://discourse.julialang.org/t/improving-doc-for-display-print-show-repr/69124/4),
the `print(x)` and `repr(x)` docstrings say that they default to calling
`show`, but don't specifically say that they call the 2-argument `show`.
(Probably because they pre-date the 3-argument `show`).
