Design Roslyn-based GenAPI Backend

[andriipatsula]

Goals & Motivation:

Our primary goal here is to provide solution suitable not just to solve our problem (better tooling for reference package generation), but also it should be good enough for other teams that depend on Microsoft.CCi.Extension like:

• AsmDiff
• ApiCompat
• Api-Diff

Below is a diagram of *Writers classes in Microsoft.CCi.Extension, they are used by GenAPI and tools listed above. Orange labeled classes/interfaces is heavily dependent on Microsoft.CCi and Blue one - less or not at all and we may reuse them. The main goal is to implement new interfaces/classes (to replace Orange) that could be easily used for:

• AsmDiff/DiffCsvWriter
• AsmDiff/DiffCSharpWriter
• AsmDiff/ApiRecordingCSharpDiffWriter

Marked as Dark - is not used by GenAPI and won't be implemented/adapted to use Microsoft.CodeAnalysis.