6246: Follow symlinks when walking project trees r=lnicola a=dfoxfranke
Fixes#3691.
~~WIP pending further testing~~:
- [X] Verify that symlinked files get indexed.
- [x] Verify that files in symlinked directories get indexed.
- [x] Verify that inotify events are properly received and handled when the target of a symlink resides outside the project tree.
Co-authored-by: Daniel Fox Franke <dfoxfranke@gmail.com>