make abi_unsupported_vector_types a hard error

[RalfJung]

Fixes #116558 by completing the transition; see that issue for context. The lint was introduced with Rust 1.84 and this has been shown in cargo's future breakage reports since Rust 1.85, released 6 weeks ago, and so far we got 0 complaints by users. There's not even a backlink on the tracking issue. We did a crater run when the lint was originally added and found no breakage. So I don't think we need another crater run now, but I can do one if the team prefers that.

#131800 is done, so for most current targets (in particular, all tier 1 and tier 2 targets) we have the information to implement this check (modulo the targets where we don't properly support SIMD vectors yet, see the sub-issues of #116558). If a new target gets added in the future, it will default to reject all SIMD vector types until proper information is added, which is the default we want.

This will need approval by for @rust-lang/lang. Cc @workingjubilee @veluca93

try-job: test-various
try-job: armhf-gnu
try-job: dist-i586-gnu-i586-i686-musl