Create a workflow for frontend checks.

This performs linting, format checks, runs tests, checks types, and
verifies prod builds. It does everything in a single job to simplify
setup (everything runs quickly so no need for multiple jobs).

Each check step always runs. If any check fails, the "Frontend Check"
check fails on PR's.

.github/workflows/frontend-checks.yml

@@ -0,0 +1,59 @@
+name: Frontend Checks
+
+on:
+  push:
+    paths:
+      - frontend/**
+  pull_request:
+    paths:
+      - frontend/**
+
+env:
+  NODE_VERSION: 14.x
+
+jobs:
+  build:
+    name: Checks
+    runs-on: ubuntu-latest
+
+    defaults:
+      run:
+        working-directory: frontend
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v2
+      - name: Cache node modules
+        uses: actions/cache@v2
+        env:
+          cache-name: cache-node-modules
+        with:
+          # npm cache files are stored in `~/.npm` on Linux/macOS
+          path: ~/.npm
+          key: ${{ runner.os }}-build-${{ env.cache-name }}-${{ hashFiles('**/package-lock.json') }}
+          restore-keys: |
+            ${{ runner.os }}-build-${{ env.cache-name }}-
+            ${{ runner.os }}-build-
+            ${{ runner.os }}-
+      - name: Use Node.js ${{ env.NODE_VERSION }}
+        uses: actions/setup-node@v1
+        with:
+          node-version: ${{ env.NODE_VERSION }}
+      - name: Install dependencies
+        run: npm ci
+
+      - name: Linting
+        if: always()
+        run: npm run lint
+
+      - name: Formatting
+        if: always()
+        run: npm run check-formatting
+
+      - name: Jest Tests
+        if: always()
+        run: npm run test
+
+      - name: Types and Production Build
+        if: always()
+        run: npm run build -- --no-lint