Rollup merge of #81720 - klensy:smallvec-update, r=Mark-Simulacrum

Updated smallvec version due to RUSTSEC-2021-0003

Hi.

Updated Cargo.toml's for smallvec due to RUSTSEC-2021-0003 and Cargo.toml in separate commit.

Affected function `SmallVec::insert_many` looks like don't was used directly in rust, but can be somewhere in deps.

There should be some mechanism to not to do this kind of things manually, like dependabot. Actually, dependabot supports rust and can check security articles (at least that noted in description).