Introduce PHP CS to improve code quality (matomo-org#16755)

* Adds PHP CS with a basic config

* automatically check coding style for pull requests

* Disallow usage of eval & create_function and force using Common::safe_unserialize instead of unserialize

* Forbid inline control structures

* fix test

Author: sgiehl

.github/workflows/phpcs.yml

@@ -0,0 +1,17 @@
+name: PHPCS check
+
+on: pull_request
+
+jobs:
+  phpcs:
+    name: PHPCS
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - name: Install dependencies
+        run: composer install --dev --prefer-dist --no-progress --no-suggest
+      - name: PHPCS check
+        uses: chekalsky/phpcs-action@v1
+        with:
+          phpcs_bin_path: './vendor/bin/phpcs'
+          enable_warnings: true

composer.json

@@ -61,7 +61,9 @@
     },
     "require-dev": {
         "lox/xhprof": "dev-master",
+        "mayflower/mo4-coding-standard": "~6.0",
         "phpunit/phpunit": "~8.5",
+        "squizlabs/php_codesniffer": "^3.5",
         "symfony/var-dumper": "~2.6.0",
         "symfony/yaml": "~2.6.0"
     },