Use more generics in datetime symbols code

[Manishearth]

Currently we use a pile of macros to define datetime symbols provider structs and datetime symbols datagen, defining this tree of "format vs standalone" + short/wide/narrow/abbreviated for each.

This is annoying to evolve, hard to debug, and leads to a proliferation of similar types. It would be nice to use generic code instead, with some internal traits to help implementation.

Most of these changes are internal aside from provider changes

Tracking:

• Remove cldr_serde::ca macros Make datagen datetime symbols code generic, add monthPatterns parsing #3767
• Make ZeroFrom work on types with borrowing generics Expand ZeroFrom to cover cases where attrs can borrow #3770
• Make Yoke work on types with borrowing generics #4119
• Move provider symbols over to something generic, typedeffing the old types for backcompat (this is a publicly visible change)
• Move datagen transform code over to using the provider generics

[sffc]

Might be obsoleted by #3865