Pkg don't use startup.jl when building and testing (#29364)
* don't use startup.jl when precompiling, building and testing (#470)
unless the user has explicitly asked for it with
--startup-file=yes
(cherry picked from commit 40d7f27f2ff08ec466df536f267129a9f5e950b4)
* do not precompile packages that have opt out to precompilation
(cherry picked from commit 57f7380a2641944be12695e92a3ad9f4cc20e6f2)
