Fluent, with all the icu4x it brings in, takes quite some time to
compile. `fluent_messages!` is only needed in further downstream rustc
crates, but is blocking more upstream crates like `rustc_index`. By
splitting it out, we allow `rustc_macros` to be compiled earlier, which
speeds up `x check compiler` by about 5 seconds (and even more after the
needless dependency on `serde_json` is removed from
`rustc_data_structures`).
Since RFC 3052 soft deprecated the authors field anyway, hiding it from
crates.io, docs.rs, and making Cargo not add it by default, and it is
not generally up to date/useful information, we should remove it from
crates in this repo.
This gives compiler maintainers a better degree of control
over how the version gets parsed and is a good way to ensure
that there are no changes of behaviour in the future.
Also, issue a warning if the version is invalid instead of erroring
so that we stay forwards compatible with possible future changes
of the versioning scheme.
Last, this improves the present test a little.
