Make Pkg.precompile work with glue packages

[IanButterworth]

Builds on #3264

(While I was here I added some comments to Pkg.precompile too, in a separate commit)

shell> rm -rf ~/.julia/compiled/v1.10

julia> import Pkg
[ Info: Precompiling Pkg [44cfe95a-1eb2-52ea-b672-e2afdf69b79f]

(Pkg) pkg> activate /Users/ian/Documents/GitHub/GluePkgExamples.jl/HasDepWithGluePkgs.jl
  Activating project at `~/Documents/GitHub/GluePkgExamples.jl/HasDepWithGluePkgs.jl`

(HasDepWithGluePkgs) pkg> precompile
Precompiling environment...
  6 dependencies successfully precompiled in 3 seconds

julia> using HasDepWithGluePkgs

julia> HasDepWithGluePkgs.do_something()
[ Info: First do something with the basic array support in B
┌ Info: HasGluePkgs.jl: A custom logging method for AbstractArray
│   x =
│    2-element Vector{Float64}:
│     0.22960852293312484
└     0.5867772603987441
[ Info: Now do something with extended OffsetArray support in B
┌ Info: HasGluePkgs.jl: A custom logging method for AbstractArray
│   x =
│    2-element OffsetArray(::Vector{Float64}, 0:1) with eltype Float64 with indices 0:1:
│     0.09267832976119839
└     0.38042557254693776

Tested on KristofferC/ExtensionExamples.jl#1

Todo

• Add tests

[KristofferC]

Add tests

This should get tested by the existing Glue package tests (since the glue packages will get precompiled there in the Pkg.develop)

[KristofferC]

[KristofferC]

I think that there will be quite a lot of collisions with glue package names, so maybe it is worth to write it in the progress output as Parent -> GluePackage or something so you can keep track from which parent package the glue package comes from?