Speed up JS linting (#2709)

* Install Prettier only, instead of all deps

* Allow running on workflow dispatch

Allows manually triggered CI runs by org members

* Update Node to latest LTS; update step descriptions

framework/core/.github/workflows/lint.yml

@@ -1,6 +1,7 @@
 name: Lint
 
 on:
+  workflow_dispatch:
   push:
     paths:
       - 'js/src/**'
@@ -10,22 +11,18 @@ on:
 
 jobs:
   prettier:
+    name: JS / Prettier
     runs-on: ubuntu-latest
 
-    name: JS / Prettier
-
     steps:
-      - uses: actions/checkout@master
+      - name: Check out code
+        uses: actions/checkout@master
 
-      - name: Setup Node.js
-        uses: actions/setup-node@v1
+      - name: Set up Node
+        uses: actions/setup-node@v2
         with:
-          node-version: "12"
+          node-version: "14"
 
-      - name: Install JS dependencies
-        run: npm ci
-        working-directory: ./js
-
-      - name: Check JS code for formatting
-        run: node_modules/.bin/prettier --check src
+      - name: Check JS formatting
+        run: npx prettier --check src
         working-directory: ./js