ResolverError coloring should be decided in showerror, not on construction

[danielwe]

A ResolverError has color hardcoded in the message if stderr supports color, as the message is formatted on construction using the following function:

Pkg.jl/src/Resolve/graphtype.jl

Lines 571 to 576 in 8b2c0f3

	function logstr(pkgID, args...)
	# workout the string with the color codes, check stderr to decide if color is enabled
	return sprint(args; context=stderr::IO) do io, iargs
	printstyled(io, iargs...; color=pkgID_color(pkgID))
	end
	end

This is unfortunate when the error message isn't actually printed to stderr, for example in Pluto:

Perhaps it would be better to store data rather than a preformatted message in the ResolverError object, and only format the message in the showerror(io, ::ResolverError) method, with or without color depending on io.

[danielwe]

The most straightforward solution here is perhaps to use 1.11's new StyledStrings stdlib