Auto merge of #50306 - alexcrichton:inline-policy, r=sfackler

std: Inline `DefaultResizePolicy::new`

This should allow us to tighten up the [codegen][example] a bit more, avoiding a
function call across object boundaries in the default optimized case.

[example]: https://play.rust-lang.org/?gist=c1179088b0f8a4dcd93a9906463f993d&version=stable&mode=release