Pkg: Allow configuring can_fancyprint(io::IO) using IOContext (#58887)

(cherry picked from commit c0cc1e1)

Author: fonsp

base/precompilation.jl

@@ -342,7 +342,7 @@ Base.show(io::IO, err::PkgPrecompileError) = print(io, "PkgPrecompileError: ", e
 
 import Base: StaleCacheKey
 
-can_fancyprint(io::IO) = io isa Base.TTY && (get(ENV, "CI", nothing) != "true")
+can_fancyprint(io::IO) = @something(get(io, :force_fancyprint, nothing), (io isa Base.TTY && (get(ENV, "CI", nothing) != "true")))
 
 function printpkgstyle(io, header, msg; color=:light_green)
     printstyled(io, header; color, bold=true)