Investigate using PolyType to simplify the ICsvRecord source generator

[joelverhagen]

We do several things in the Source Generator in this project:

• Generate CSV read and write method
• Generate Kusto DDL and data mapping
• Generate MessagePack formatters

I discovered PolyType while trying out https://github.com/AArnott/Nerdbank.MessagePack.

Maybe PolyType can be used to simplify the Source Generator.

#118 should be considered at the same time.