Switch to pnpm

[NullVoxPopuli]

Context, Plan, etc: https://gist.github.com/NullVoxPopuli/eafc7dad6547de5e730098498b829e1f

Requires that this be merged first:

• V2 Addon conversion prep: convert to single-package monorepo. #1060

Due to errors discovered in the test-app extraction PR, here: #1061
It was determined that yarn is insufficient for ember-qunit.

This PR migrates the repo to pnpm.

Afterwards, the following are unblocked (in-order):

1. Extract test app #1062
2. Convert to native package #1064

[ijlee2]

nitpick

At this stage, we don't have the test-app package yet. I'd have added line 3 in #1062. We can merge this PR as is, since (I think) pnpm ignores entries corresponding to packages that don't exist yet.

[ijlee2]

nitpick

In #1060, I noticed you had to update the volta entry in the root package.json.

ember-qunit/package.json

Lines 15 to 18 in 5862d31

	"volta": {
	"node": "16.20.0",
	"yarn": "1.22.19"
	}

I'm guessing that, in this pull request, the entry should have similarly been updated again, by replacing yarn with pnpm? (Maybe this happens in a later PR. At any rate, we can merge the PR as is.)

[NullVoxPopuli]

Nice catch! Thanks!
For conflict management, i'd like to do that in the test-app extraction pr.

[NullVoxPopuli]

At this stage, we don't have the test-app package yet.

I missed this comment.

I extracted code from PR #1062 -- this this #1063, is meant for easier review of the whole process only, and isn't itself an atomic change.