### Purpose
This fixes#9775. I also improved the comments as they were lacking.
My apologies for introducing this bug. In summary, the bug was
```
mode = mode ^ (ModeSymlink | ModeIrregular)
```
didn't correctly reset those bits. This correctly resets them:
```
mode = mode &^ ModeSymlink &^ ModeIrregular
```
Tested and working in Windows 11 version 10.0.22631.4317. I didn't test
in other versions, but I'm sure this is the only issue.
### Purpose
Deduplicated files are apparently considered 'irregular' under the hood,
this causes them to simply be ignored by Syncthing. This change is more
of a workaround than a proper fix, as the fix should probably happen in
the underlying libraries? - which may take some time. In the meanwhile,
this change should make deduplicated files be treated as regular files
and be indexed and synced as they should.
### Testing
Create some volume where deduplication is turned on (see the relevant
issue for details, including a proper description of how to reproduce
it). Prior to this change, the deduplicated files were simply ignored
(even by the indexer). After this change, the deduplicated files are
being index and synced properly.
