Migrate to pnpm

in order to avoid ember-source `peerDependency` being hoisted to the
root node_modules, which causes unreliable imports in embroider.

see: embroider-build/embroider#1169 (comment)

Also:

- [Breaking] Drop Node@12 support due to `pnpm` requires it
- Use slightly dated pnpm@7.5.2, since in the later version there are
  issues with `--frozen-lockfile` installations

.github/workflows/ci.yml

@@ -18,28 +18,30 @@ jobs:
 
     steps:
       - uses: actions/checkout@v3
+
       - name: Install Node
         uses: actions/setup-node@v3
         with:
-          node-version: 12.x
-          cache: npm
+          node-version: 14.x
 
-      - name: npm8
-        run: npm install -g npm@8
+      - uses: pnpm/action-setup@v2.2.2
+        with:
+          version: 7.5.2
+          run_install: false
 
-      - name: Install Dependencies
-        run: npm ci
+      - name: Install dependencies
+        run: pnpm install
 
       - name: Lint Addon
-        run: npm run lint
+        run: pnpm lint
         working-directory: addon
 
       - name: Lint Test App
-        run: npm run lint
+        run: pnpm lint
         working-directory: test-app
 
       - name: Run Tests
-        run: npm run test:ember
+        run: pnpm test:ember
         working-directory: test-app
 
   floating:
@@ -49,23 +51,26 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        node-version: [12.x, 14.x]
+        node-version: [14.x, 16.x]
 
     steps:
       - uses: actions/checkout@v3
-      - uses: actions/setup-node@v3
+
+      - name: Install Node
+        uses: actions/setup-node@v3
         with:
-          node-version: ${{ matrix.node-version }}
-          cache: npm
+          node-version: 14.x
 
-      - name: npm8
-        run: npm install -g npm@8
+      - uses: pnpm/action-setup@v2.2.2
+        with:
+          version: 7.5.2
+          run_install: false
 
       - name: Install Dependencies
-        run: npm install --no-package-lock
+        run: pnpm install --frozen-lockfile=false
 
       - name: Run Tests
-        run: npm run test:ember
+        run: pnpm test:ember
         working-directory: test-app
 
   node-tests:
@@ -75,23 +80,26 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        node-version: [12.x, 14.x, 16.x]
+        node-version: [14.x, 16.x]
 
     steps:
       - uses: actions/checkout@v2
-      - uses: actions/setup-node@v2
+
+      - name: Install Node
+        uses: actions/setup-node@v3
         with:
-          node-version: ${{ matrix.node-version }}
-          cache: npm
+          node-version: 14.x
 
-      - name: npm8
-        run: npm install -g npm@8
+      - uses: pnpm/action-setup@v2.2.2
+        with:
+          version: 7.5.2
+          run_install: false
 
       - name: Install Dependencies
-        run: npm ci
+        run: pnpm install
 
       - name: Run Tests
-        run: npm run test
+        run: pnpm test
         working-directory: addon
 
   try-scenarios:
@@ -118,15 +126,16 @@ jobs:
       - name: Install Node
         uses: actions/setup-node@v2
         with:
-          node-version: 12.x
-          cache: npm
+          node-version: 14.x
 
-      - name: npm8
-        run: npm install -g npm@8
+      - uses: pnpm/action-setup@v2.2.2
+        with:
+          version: 7.5.2
+          run_install: false
 
       - name: Install Dependencies
-        run: npm ci
+        run: pnpm install
 
       - name: Run Tests
-        run: ../node_modules/.bin/ember try:one ${{ matrix.try-scenario }}
+        run: ./node_modules/.bin/ember try:one ${{ matrix.try-scenario }}
         working-directory: test-app

.npmrc

@@ -0,0 +1 @@
+strict-peer-dependencies=false

addon/package.json

@@ -47,7 +47,7 @@
     "test": "mocha node-tests --recursive"
   },
   "dependencies": {
-    "@embroider/addon-shim": "^1.6.0",
+    "@embroider/addon-shim": "^1.8.0",
     "@ro0gr/ceibo": "^2.2.0",
     "@types/jquery": "^3.5.14",
     "jquery": "^3.5.1"
@@ -57,7 +57,7 @@
     "@babel/eslint-parser": "^7.17.0",
     "@babel/plugin-proposal-class-properties": "^7.16.7",
     "@babel/plugin-proposal-decorators": "^7.17.9",
-    "@embroider/addon-dev": "^1.6.0",
+    "@embroider/addon-dev": "^1.8.0",
     "@rollup/plugin-babel": "^5.3.1",
     "chai": "^4.1.2",
     "ember-cli-blueprint-test-helpers": "^0.18.2",
@@ -68,7 +68,8 @@
     "eslint-plugin-prettier": "^4.0.0",
     "mocha": "^4.0.1",
     "prettier": "^2.6.2",
-    "rollup": "^2.71.1"
+    "rollup": "^2.71.1",
+    "npm-run-all": "^4.1.5"
   },
   "peerDependencies": {
     "@ember/test-helpers": "^2.5.0",