Support round-tripping parameter names from function type definitions

[tlively]

Although the name section already supports naming parameters from function definitions, it does not support naming parameters from function type definitions, and so far this proposal does not support that either. If our goal is to be able to round trip all names in the text format (even those that cannot be used), we should add support for these documentary parameter names to this proposal.

Naming function type parameters is very similar to naming struct and array type fields. Support for field naming is added in the GC proposal, and in principal parameter names could be added there as well, but since that proposal is almost at phase 4 and there is no design or implementation for parameter names, it would be better to add support for those in this proposal instead.