Auto merge of #151076 - cuviper:compiler-hashbrown-0.16.1, r=Amanieu

compiler: upgrade to hashbrown 0.16.1

See also rust-lang/rust#135634, rust-lang/rust#149159, and rust-lang/hashbrown#662.

This includes an in-tree upgrade of `indexmap` as well, which uses the
new `HashTable` buckets API internally, hopefully impacting performance
for the better.

And finally, we can remove `#[rustc_unsafe_specialization_marker]` on `Copy`!

cc @joboet
r? @Amanieu

Author: bors