CBOR: Basic Support for Tags

[JesusMcCloud]

Introduces basic support for CBOR tags.

Basic means that no semantic checks are performed yet, so you freely use reserved tags (e.g. serialize a cornucopia of fruit and other produce using tags reserved for dates, URIs, MIME messages, negative bignums and so forth) and no error will be thrown.

• New annotations ValueTags and KeyTags to specify tags for keys and values, respectively
  • Tags can be nested freely as specified in the annotations
  • By default, tags will be validated upon deserialization. If no annotations are present on a property, validation is omitted. Behaviour can be customized (see below).
  • By default, tags will be written as annotated. Behaviour can be customized (see below).
• Introduces the following configuration parameters to the Cbor class (names are self-explanatory):
  • writeKeyTags
  • writeValueTags
  • verifyKeyTags
  • verifyValueTags

This is the first PR in a series of planned enhancements, but we still consider it valuable on its own (as it also affects Kotlin#1560).

In the long run, we plan to support semantically correct serialization for all reserved CBOR tags. This includes separate contributions to koltinx.datetime and the native support for self-describing CBOR. The latter of which is planned to enable the deserialization of CBOR structures, while also enabling access to the original underlying raw byte-string. This is a crucial features for conveniently working with (i.e. verifying) signed data. (Which, in turn, is a requirement for a 100% pure Kotlin multiplatform COSE implementation.)
Hence, we want to use this opportunity to also collect early feedback from those who are more familiar with kotlinx.serialization than we are.

[nodh]

Works great, but small changes requested

[JesusMcCloud]

submitting to upstream