how to work with relative paths with $PROJECT_DIR$ keyword Follow

Hi,
I'm writing a pugin, which stores paths of some files to IPR file. I want to
save these paths as relative to project directory. Is there any way to
convert absolute path to relative path with $PROJECT_DIR$ keyword?

file://C:/AURORA/projects/rba/src/somefile.txt

to

file://$PROJECT_DIR$/src/somefile.txt


I'm try to use VfsUtil.getRelativePath, but this method gets only the
relative path to ancestor dir. Not include $PROJECT_DIR$ keyword.

Thank you

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