Parent name of extension not shown in precompilation finished message

[JoshuaLampert]

The docs currently suggest to name extensions without including the parent name because "extension names are always shown together with their parent package name". This is not true though as the following example shows:

julia> using KernelInterpolation

julia> using Meshes
Precompiling KernelInterpolationMeshesExt finished.
  1 dependency successfully precompiled in 2 seconds. 259 already precompiled.

I would prefer to see

julia> using KernelInterpolation

julia> using Meshes
Precompiling KernelInterpolation → KernelInterpolationMeshesExt finished.
  1 dependency successfully precompiled in 2 seconds. 259 already precompiled.

(in this case I would also rename the extension to MeshesExt following the docs)

For stacktraces, we currently see something like

ERROR: test error
Stacktrace:
 [1] error(s::String)
   @ Base ./error.jl:44
 [2] NodeSet(points::PointSet{𝔼{1}, CoordRefSystems.Cartesian{CoordRefSystems.NoDatum, 1, Unitful.Quantity{Float64, 𝐋, Unitful.FreeUnits{…}}}, Vector{Point{𝔼{…}, CoordRefSystems.Cartesian{…}}}})
   @ KernelInterpolationMeshesExt ~/.julia/dev/KernelInterpolation/ext/KernelInterpolationMeshesExt.jl:15
 [3] top-level scope
   @ REPL[5]:1
Some type information was truncated. Use `show(err)` to see complete types.

It also only shows the extension name without the parent name, but it includes the path, which in turn usually includes the parent name. So probably that's fine. This is also how I understand JuliaLang/Pkg.jl#3600 (comment). I wanted to mention it here nevertheless.

This came from a discussion on Zulip @aplavin @JamesWrigley.