Initial commit. Re-factored AbstractAddParametercodeFixProvider to reuse insert position logic. First simple C# tests.

The [change](https://github.com/dotnet/roslyn/commit/6be56fadb4c417c4b6af0bf62f1242e41c8dd124) to move analyzers to 2.5 version broke analyzers in the branch - they are laid out differently in the new nuget package. Build targets are unable to find the props for importing the analyzers and silently bail out executing them. This PR fixes the following:

1. Fix the props file path in Imports.Targets
2. Move to a newer analyzer package which has an important [bug fix](https://github.com/dotnet/roslyn-analyzers/pull/1255)
3. Report a build error if analyzer props file does not exist
4. Fix the public API errors (mostly due to duplicate entries in shipped and unshipped files).
5. Fix one instance of RS0014 (Do not use Enumerable methods on indexable collections. Instead use the collection directly) introduced recently in the code.
6. Add suppression for one instance of CA1802 in WellKnownAttributeData.cs that fixed the signing issue.