Enable corepack in CI

[jakebailey]

In lieu of actions/setup-node#531, enable this by hand.

I'm pretty sure this works. If it doesn't, everything will fail and that'll tell me everything I need.

[fatcerberus]

The fact that we need a separate package manager to manage package managers is crazy; let's see how long until that space also gets fragmented and then we need a package manager manager manager...

[jakebailey]

The fact that we need a separate package manager to manage package managers is crazy; let's see how long until that space also gets fragmented and then we need a package manager manager manager...

volta, pacman, .... 😄

[sandersn]

Seems fine to try. Why do we need this?

[jakebailey]

This insulates us from the version of npm provided by the version of node that's installed, instead using the version of npm declared in package.json. Really, this only matters for anything that intends to actually modify package.json or package-lock.json, so could be scoped down to just affect the update scripts, version bumpers, the release, etc, if desired, but if it were available on the setup-node action, I'd be enabling it everywhere.

Arguably, this should also be applied to the AzDo task we use to release TS to npm (non-nightly), as that's exactly what has broken us in the past; it using npm 6 which has different behavior that we use everywhere else.

[jakebailey]

I opted to remove all but the ones where it matters.