Create rule S1656: Variables should not be self-assigned (#4679)

* Add rust to rule S1656

* Update RSPEC

* Remove tag

---------

Co-authored-by: yassin-kammoun-sonarsource <yassin-kammoun-sonarsource@users.noreply.github.com>
Co-authored-by: yassin-kammoun-sonarsource <yassin.kammoun@sonarsource.com>

rules/S1656/rust/metadata.json

@@ -0,0 +1,5 @@
+{
+  "tags": [
+    "clippy"
+  ]
+}

rules/S1656/rust/rule.adoc

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+== Why is this an issue?
+
+include::../description.adoc[]
+
+=== Noncompliant code example
+
+[source,rust,diff-id=1,diff-type=noncompliant]
+----
+let mut x = 5;
+x = x; // Self-assignment - does nothing
+----
+
+==== Compliant solution
+
+[source,rust,diff-id=1,diff-type=compliant]
+----
+let mut x = 5;
+// Removed the self-assignment
+----
+
+== Resources
+=== Documentation
+
+* Clippy Lints - https://rust-lang.github.io/rust-clippy/master/index.html#self_assignment
+
+ifdef::env-github,rspecator-view[]
+
+'''
+== Implementation Specification
+(visible only on this page)
+
+include::../message.adoc[]
+
+'''
+== Comments And Links
+(visible only on this page)
+
+include::../comments-and-links.adoc[]
+
+endif::env-github,rspecator-view[]