update to removal of SourceManager::createFileID(FileEntry*)
The overload of SourceManager::createFileID taking
a FileEntry * was removed in LLVM commit
llvmorg-18-init-7647-g27254ae51192
([clang] NFCI: Use `FileEntryRef` for `FileID` creation (#67838),
Tue Oct 3 22:07:46 2023 +0200).
Use FileManager::getFileRef instead of FileManager::getFile
whenever FileManager::getFileRef is available
so that the overload of SourceManager::createFileID taking a FileEntryRef
can be used.
Signed-off-by: Sven Verdoolaege <sven.verdoolaege@gmail.com>