Create rule S6647: Unnecessary constructors should be removed (#2243)

https://github.com/SonarSource/SonarJS/issues/3906

rules/S6647/javascript/metadata.json

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+{
+  "title": "Unnecessary constructors should be removed",
+  "type": "CODE_SMELL",
+  "status": "ready",
+  "remediation": {
+    "func": "Constant\/Issue",
+    "constantCost": "5min"
+  },
+  "tags": [
+  ],
+  "defaultSeverity": "Minor",
+  "ruleSpecification": "RSPEC-6647",
+  "sqKey": "S6647",
+  "scope": "All",
+  "defaultQualityProfiles": ["Sonar way"],
+  "quickfix": "covered"
+}

rules/S6647/javascript/rule.adoc

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+== Why is this an issue?
+
+If the class declaration does not include a constructor, one is automatically created, so there is no need to provide an empty constructor, or one that just delegates to the parent class.
+
+[source,javascript]
+----
+class Foo {
+    constructor() {}  // Noncompliant, empty
+}
+
+class Bar extends Foo {
+    constructor(params) { // Noncompliant, just delegates to the parent
+        super(params);
+    } 
+}
+----
+
+Instead, you can safely remove the empty constructor without affecting the functionality.
+
+[source,javascript]
+----
+class Foo {}
+
+class Bar extends Foo {}
+----
+
+== Resources
+=== Documentation
+
+* https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes/constructor[MDN - constructor]

rules/S6647/metadata.json

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+{
+}