Code Intelligence for C#

Proposal

Add Code Intelligence for C#. Note that other languages are discussed in the Code Intelligence epic &4212, but not C# at this time.

Note that we are a new, relatively large, Premium subscriber to GitLab.com (SaaS) that has many millions of lines of C# code. We had Code Intelligence/Navigation functionality both in GitHub and Azure Repositories, but are now sadly finding this isn't supported in GitLab.