Certain functions can not be called while precompiling

[KristofferC]

See the discourse post https://discourse.julialang.org/t/plots-breaks-incremental-compilation/96990/3. This @eval call does not work during precompilation.

In general, I am a bit scared about all the @evals (even into Main) that Plots.jl does. I am sure there are reasons for it but would be good to try reduce it as much as possible probably.

[t-bltg]

It's already reduced, I guess, this has also bothered me for a while.
This is induced by Plots initial design of having optional backends (we are forced to @eval in Main, else Pkg will complain about a backend not being a Plots dependency), and I don't think there is a trivial enhancement to this if we want to retain compatibility with previous julia versions.
Maybe we can use weak deps following #4649 in julia 1.9, but that's a lot of work and breaking for sure, so reserved for Plots 2.0.