Fixes name generation for nested anonymous types

[dpaoliello]

Fixes the following issues with name generation for nested anonymous types:

• A numeral would only be appended if the parent had more than one anonymous records, but an anonymous typed array didn't count as a record resulting in multiple structs named _Anonymous_e__Struct.
• The code that remapped the name of anonymous types was different between the code that generated the type definition and the code that defined fields in a FixedBuffer.
• When nesting more than one level of anonymous types, the name of the nested type could be the same as the parent type which is not permitted in C# (error CS0542: '_Anonymous_e__Struct': member names cannot be the same as their enclosing type).