[RFC] Plots `2.0`

Too many issues need stuff discussed but postponed to 2.0 because rightfully considered breaking. Latest example at https://github.com/JuliaPlots/Plots.jl/issues/4561, caused by a cycling bug identified more than two years ago in https://github.com/JuliaPlots/Plots.jl/issues/2980.

Should we branch somehow and start working on 2.0 ?

I've closed around ~80 stale issues this we, we need to go through all the remaining opened issues, close the stale ones (or won't fix because of an upstream problem, or dependencies), apply labels to start focusing on important things (like scaling, fonts, backend selection, precompilation, consistency between backends, ...). We won't do this on our own, so please do join this attempt.

Labeled issues:

• https://github.com/JuliaPlots/Plots.jl/issues/4532
• https://github.com/JuliaPlots/Plots.jl/issues/4028
• https://github.com/JuliaPlots/Plots.jl/issues/3001
• https://github.com/JuliaPlots/Plots.jl/issues/2980
• https://github.com/JuliaPlots/Plots.jl/issues/2129
• https://github.com/JuliaPlots/Plots.jl/issues/2047
• https://github.com/JuliaPlots/Plots.jl/issues/4181
• https://github.com/JuliaPlots/Plots.jl/issues/4513
• https://github.com/JuliaPlots/Plots.jl/issues/4631
• https://github.com/JuliaPlots/Plots.jl/issues/4350
• https://github.com/JuliaPlots/Plots.jl/issues/4567
• https://github.com/JuliaPlots/Plots.jl/issues/4596

Labeled PRs:

• https://github.com/JuliaPlots/Plots.jl/pull/4326
• https://github.com/JuliaPlots/Plots.jl/pull/3942
• https://github.com/JuliaPlots/Plots.jl/pull/3744
• https://github.com/JuliaPlots/Plots.jl/pull/3732
• https://github.com/JuliaPlots/Plots.jl/pull/3473
• https://github.com/JuliaPlots/Plots.jl/pull/3357
• https://github.com/JuliaPlots/Plots.jl/pull/3351