Add PHPCS.

.github/workflows/phpcs.yml

@@ -0,0 +1,24 @@
+name: Drupal coding standards
+
+on: pull_request
+
+jobs:
+  phpcs:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: shivammathur/setup-php@verbose
+        with:
+          php-version: 8.1
+          coverage: none
+          tools: composer:v2, cs2pr, dealerdirect/phpcodesniffer-composer-installer:*, drupal/coder
+      - name: Get composer cache directory
+        id: composercache
+        run: echo "::set-output name=dir::$(composer config cache-files-dir)"
+      - uses: actions/cache@v2
+        with:
+          path: ${{ steps.composercache.outputs.dir }}
+          key: ${{ runner.os }}-composer-${{ hashFiles('**/composer.json') }}
+          restore-keys: ${{ runner.os }}-composer-
+      - name: Detect coding standard violations
+        run: phpcs -q --report=checkstyle | cs2pr --graceful-warnings

phpcs.xml.dist

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+<?xml version="1.0" encoding="UTF-8"?>
+<ruleset name="civicrm_entity">
+  <description>PHP CodeSniffer configuration for CiviCRM entity.</description>
+  <file>.</file>
+  <arg name="extensions" value="php,module,inc,install,test,profile,theme,info,yml"/>
+
+  <exclude-pattern>*/vendor/*</exclude-pattern>
+  <exclude-pattern>*/node_modules/*</exclude-pattern>
+
+  <rule ref="Drupal"/>
+  <rule ref="DrupalPractice"/>
+</ruleset>