Split HTTP::Cookies.from_headers into separate methods for server/client

[straight-shoota]

HTTP::Cookies.from_headers populates a Cookie collection from HTTP headers. It parses both Cookie and Set-Cookie headers, which seems odd. They are distinct features you really never want to use in combination (you can't have both in the same set of headers).
In practice it means HTTP::Client accepts cookies defined by Cookie header and HTTP::Server accepts cookies defined by Set-Cookie header. Both is very confusing and could even offer an opportunity for abuse by circumventing the correct header mechanincs.

This patch deprecates {fill_,}from_headers and replaces it with distinct {fill_,}from_client_headers and {fill_,}from_server_headers methods.

[sdogruyol]

Thank you @straight-shoota 🙏