Skip symbolic links when passing files to Prettier
- Fix#6378
- [`lib/functions/detectFiles.sh`]: Add `IsNotSymbolicLink()` function
to check whether provided file is symbolic link or not
- [`lib/functions/buildFileList.sh`]: Use `IsNotSymbolicLink()` function
to not add files that are symbolic links to the file array for
Prettier
- [`test/lib/detectFilesTest.sh`]: Add test for `IsNotSymbolicLink()`
function
- Add `test/linters/prettier/test_symlink_good.md` file symlinked into parent
dir's `README.md` to test it is skipped from Prettier (also exclude
its directory from JSCPD to suppress error about cloned content)