Add structured header parser

### Is there an existing issue for this?

- [X] I have searched the existing issues

### Is your feature request related to a problem? Please describe the problem.

I'm working on adding support for [User Agent Client Hints](https://web.dev/user-agent-client-hints/) in our apps; the contents of the `sec-ch-ua` header follows for the [format covered by this draft RFC](https://tools.ietf.org/id/draft-ietf-httpbis-header-structure-15.html). Adding support for User Agent Client Hints would be easy if ASP.NET had such a header parser.

### Describe the solution you'd like

Provide a public header class that supports structured header formatting - eg something like `public class StructuredHeaderValue`. While writing such a parser shouldn't be too difficult given the [strict format](https://tools.ietf.org/id/draft-ietf-httpbis-header-structure-15.html#strict), it would be preferable if it was part of the framework - please consider adding it.

You likely have a policy not to invest in code, especially public APIs, when the RFC isn't ratified. That makes sense, but User Agent Client Hints are out, and they're built on it.

### Additional context

Probably related to #31492