[wpmlbridge-296] Bring PHPStan analysis.

https://onthegosystems.myjetbrains.com/youtrack/issue/wpmlbridge-296

composer.json

@@ -28,22 +28,26 @@
     "config": {
         "sort-packages": true,
         "platform": {
-            "php": "5.6"
+            "php": "7.4"
         },
         "allow-plugins": {
-            "dealerdirect/phpcodesniffer-composer-installer": true
+            "dealerdirect/phpcodesniffer-composer-installer": true,
+            "phpstan/extension-installer": true
         }
     },
     "minimum-stability": "dev",
     "prefer-stable": true,
     "require-dev": {
-        "roave/security-advisories": "dev-master",
+        "dealerdirect/phpcodesniffer-composer-installer": "*",
         "otgs/unit-tests-framework": "~1.2.0",
-        "sebastian/phpcpd": "^3.0",
-        "squizlabs/php_codesniffer": "~3",
         "phpcompatibility/php-compatibility": "*",
         "phpcompatibility/phpcompatibility-wp": "*",
-        "dealerdirect/phpcodesniffer-composer-installer": "*",
+        "phpstan/extension-installer": "^1.3",
+        "phpstan/phpstan": "^1.10",
+        "roave/security-advisories": "dev-master",
+        "sebastian/phpcpd": "^3.0",
+        "squizlabs/php_codesniffer": "~3",
+        "szepeviktor/phpstan-wordpress": "^1.3",
         "wp-coding-standards/wpcs": "^0"
     },
     "scripts": {

phpstan.neon

@@ -0,0 +1,19 @@
+parameters:
+  level: 3
+  featureToggles:
+    disableRuntimeReflectionProvider: true
+  bootstrapFiles:
+    - tests/phpstan/bootstrap.php
+    - tests/phpstan/stubs/elasticpress.stub
+    - tests/phpstan/stubs/wp-cli.stub
+  paths:
+    - src
+  dynamicConstantNames:
+    - EP_VERSION
+    - EP_DASHBOARD_SYNC
+
+  checkFunctionNameCase: true
+  inferPrivatePropertyTypeFromConstructor: true
+
+  parallel:
+    processTimeout: 300.0