Use utility methods to construct `HashMap`s and `HashSet`s

Use utility methods to construct `HashMap`s and `HashSet`s

In the next commit we'll bump the `hashbrown` version, which no
longer randomizes its hasher by default. Thus, we'll need to call
a different constructor in no-std builds from std builds.

Here we do a quick prefactor to use wrappers for constructors
instead of calling the tables directly to make the version bump
changeset smaller.