Parse fls file when searching for the root file
Parse fls file when searching for the root file

This is need when the included files use TeX macros in their names. See
https://tex.stackexchange.com/questions/289450/path-of-figures-in-different-directories-with-subfile-latex

Related to #1971

James-Yu/LaTeX-Workshop,James-Yu/LaTeX-Workshop,James-Yu/LaTeX-Workshop,James-Yu/LaTeX-Workshop,James-Yu/LaTeX-Workshop