arrow

GH-41263: [C#][Integration] Ensure offset is considered in all branches of the bitmap comparison (#41264)

### Rationale for this change

The optimization for validity buffers was still failing after https://github.com/apache/arrow/pull/41259 (sorry!).

### What changes are included in this PR?

There were still two problems:

- The offset of the actual array was not considered in the "optimized" branch
- When this offset *was* considered, it became clear that zero-length arrays were not going to work in that branch

### Are these changes tested?

I added the integration workflow to also run for C# additions. This might be a heavy CI job and I'm not sure if you want to keep it there (but running it is useful for this PR to ensure I actually fix things).

For future me (or maybe future others), the integration tests are pretty easy to check:

```
dotnet build
archery integration --run-c-data --with-csharp=true
```

### Are there any user-facing changes?

No.
* GitHub Issue: #41263

Authored-by: Dewey Dunnington <dewey@fishandwhistle.net>
Signed-off-by: Curt Hagenlocher <curt@hagenlocher.org>