fix: arglist toggle and syntax when using dirvish_relative_paths

[mrak]

Description

Setting let g:dirvish_relative_paths = 1 breaks arglist tracking and syntax highlighting.

Steps to reproduce

1. Add let g:dirvish_relative_paths = 1 into your vimrc, init.vim, or equivalent configuration file.
2. Edit an exsisting file nvim myfile
3. Open dirvish via -
   • Note that myfile is not highlighted using the DirvishArg highlight
4. Press x one or more times
   • Note that the message arglist: N files increases N with each press of x and that the syntax is not toggled

Fix

Normalize the filepath in two code sections. During the syntax detection and when invoking set_args