IDEA-77929 Convert line endings of existing file

1. Do not highlight line separator which differs from project-level line separator (the rationale is that we do not do that for different encoding);
2. Putting a local history label after 'change line separator' action was called;
3. Do not process project files and auxiliary files (e.g. '.git') during bulk 'change line separator' operation invoked on a directory(ies);