feat: add basic support for debugging and working with devcontainer

For GitHub Codespaces e.g.

.vscode/extensions.json

@@ -0,0 +1,7 @@
+{
+    "recommendations": [
+        "recca0120.vscode-phpunit",
+        "onecentlin.phpunit-snippets",
+        "devsense.profiler-php-vscode"
+    ]
+}

.vscode/launch.json

@@ -0,0 +1,35 @@
+{
+    "version": "0.2.0",
+    "configurations": [
+        {
+            "name": "Launch built-in server and debug",
+            "type": "php",
+            "request": "launch",
+            "runtimeArgs": [
+                "-S",
+                "localhost:8000",
+                "-t",
+                "."
+            ],
+            "port": 9003,
+            "serverReadyAction": {
+                "action": "openExternally"
+            }
+        },
+        {
+            "name": "Debug current script in console",
+            "type": "php",
+            "request": "launch",
+            "program": "${file}",
+            "cwd": "${fileDirname}",
+            "externalConsole": false,
+            "port": 9003
+        },
+        {
+            "name": "Listen for Xdebug",
+            "type": "php",
+            "request": "launch",
+            "port": 9003
+        }
+    ]
+}