Gaps in WASI named-import support #14858

Some gaps in WASI named-import support (add_named_to_linker):

• Labelled p2 wasi:io/{error,poll,streams} and wasi:clocks/timezone (p2 and p3) aren't in the named_imports lists in p2/bindings.rs/p3/bindings.rs, so components importing them under a label fail to link.
• wasi-keyvalue, wasi-config, wasi-tls (p2 and p3) and wasi-nn have no named support. keyvalue and config keep their bindings private, so embedders can't do it themselves with add_to_linker_instance either.
• There's no sync named API for p2 wasi or p2 http (the tests note this is intentional; mentioning it for completeness).