Use StyledStrings Faces for stacktrace printing

This allows for the faces used (e.g. the file path) to be
user-customised, which provides an escape from themes that make bright
black invisible.

base/errorshow.jl

@@ -100,9 +100,9 @@ function showerror(io::IO, ex, bt; backtrace=true)
     end
 end
 
-function stacktrace_path(file::Union{Nothing, String}, line::Union{Nothing, Int64})
+function stacktrace_path(file::Union{Nothing, String}, line::Union{Nothing, Int})
     realfile = if !isnothing(file) && file != "" && !startswith(String(file), "REPL")
-        fixup_stdlib_path(String(file))
+        String(file) |> fixup_stdlib_path |> find_source_file
     end
     pathstr = file
     if !isnothing(pathstr)
@@ -802,7 +802,8 @@ function print_stackframe(io, i, frame::StackFrame, n::Int, ndigits_max, modulec
     print(io, if inlined AnnotatedString("[inlined]", [(1:9, :face => :julia_stacktrace_inlined)]) else "" end)
 end
 
-function print_module_path_file(io, modul, file, line; modulecolor = :bright_black, digit_align_width = 0)
+function print_module_path_file(io::IO, modul::Module, file::Union{Nothing, String}, line::Union{Nothing, Int};
+                                modulecolor = :bright_black, digit_align_width = 0)
     print(io, ' ' ^ digit_align_width, AnnotatedString("@", [(1:1, :face => :julia_stacktrace_location)]))
     if modul !== nothing && modulecolor !== nothing
         mstr = string(modul)