/cc @jkotas

How do you avoid chicken-and-egg problems? does this custom attribute parser get used when you are loading some class or JITing a method? What if there was [InlineArray] data in RuntimeCustomAttributeData.cs that the parser itself depended on, for example?

@lambdageek I didn't remove the parser itself, just the infrastructure around calling the native parser from managed code. This was very old code and the process was rather complicated.

1. Partially populate, using Reflection, managed types with details for the signature parsing
2. Pass those managed types down into native via an FCall
3. Convert the data in the managed types into the native types
4. Parsing the signature blob using the details in the native types
5. Place the data from the native types into the managed types
6. Move back into managed code and lazily convert the raw details into public surface types

This PR simply collapses 2 - 5 and does it all in C#.