Use managed reflection to detect shared code

[Daniel-Svensson]

Use cecil instead of "normal" readonly reflection to detect shared code

This should allow fixing

• Should allow doing reflection on non mscorlib based targets (ex netstandard, netcoreapp ..)

• Remove old code (or allow fallback)
• Add to nuget
• Compare codegen for some targets
• Look into adding test with netstandard client for codegen tests
• Manual test of nuget for T4 codegen and standard codegen