[FR] Regression in `using` time

[ViralBShah]

I benchmarked Plots 1.4.0 with various versions of Julia for precompile, using (in a new session), and then producing a plot. At some point we had lower times.

Probably the precompile lines need a refresh - with all the new work that has been done. Maybe we should focus on 1.5.

              precompile  using    plot 
1.2.0            107         6       3
1.3.1            130         9       3
1.4.2            120        11       3
1.5-beta         144         8       2
1.6-master       120         7       2

[BeastyBlacksmith]

Would it be possible to generate the precompile files at build time, such that they don't get outdated?

[BeastyBlacksmith]

New timings in #2835 (comment)