C# Driver Language Compatibility table doesn't have .NET 5 listed

Description

The language compatibility table in the docs doesn't mention .NET 5.

We've also noticed some possible performance issues with using the 2.10.1 C# driver with our .NET 5 codebase, but that is another topic/issue on itself.

Reorganize the columns from latest to oldest.

Scope of changes 

dotnet driver has the same compatibility for .NET 5 as .NET Core 3.1

Impact to Other Docs

MVP (Work and Date)

Resources (Scope or Design Docs, Invision, etc.)