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GH-36812: [C#] Fix C API support to work with .NET desktop framework (#36813)

### What changes are included in this PR?

The C API support in the C# library has been modified to work correctly on .NET 4.7.2.
The tests have been modified to work correctly on .NET 4.7.2, though that platform is disabled by default as the Python interop seem to cause a hang when unloading the xUnit AppDomain.

**This PR contains a "Critical Fix".**
* Closes: #36812

Authored-by: Curt Hagenlocher <curt@hagenlocher.org>
Signed-off-by: Weston Pace <weston.pace@gmail.com>