add pcov extension (shared only, like xdebug)

config/ext.json

@@ -567,6 +567,13 @@
         "type": "builtin",
         "unix-only": true
     },
+    "pcov": {
+        "type": "external",
+        "source": "pcov",
+        "target": [
+            "shared"
+        ]
+    },
     "pdo": {
         "type": "builtin"
     },

config/source.json

@@ -963,6 +963,15 @@
             "path": "LICENSE"
         }
     },
+    "pcov": {
+        "type": "url",
+        "url": "https://pecl.php.net/get/pcov",
+        "filename": "pcov.tgz",
+        "license": {
+            "type": "file",
+            "path": "LICENSE"
+        }
+    },
     "pdo_sqlsrv": {
         "type": "url",
         "url": "https://pecl.php.net/get/pdo_sqlsrv",