csharp: standardize on formatting conventions

### What feature or improvement would you like to see?

There's a mix of "_field" and "this.field" in the code in addition to other formatting inconsistencies. It would be good to standardize.

Start by reviewing the C# codebase to inventory the mixed field and formatting conventions described in the issue. Identify a single convention and apply it consistently across the affected code; done means the inconsistencies are removed throughout the relevant C# sources.

Written by the indexing model from the issue text.