Create rule S6146: "Option Explicit" should be enabled (#4582)

* Add vb6 to rule S6146

* Add description

* Update description for LaYC

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Co-authored-by: thahnen <thahnen@users.noreply.github.com>
Co-authored-by: Tobi Hahnen <tobias.hahnen@sonarsource.com>

rules/S6146/vb6/metadata.json

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+{
+}

rules/S6146/vb6/rule.adoc

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+== Why is this an issue?
+
+There are several compilations options available for Visual Basic source code and `Option Explicit` defines compiler behavior for implicit variable declarations. Not specifying `Option Explicit` will allow creating a variable by it's first usage. This behavior can lead to unexpected runtime errors due to typos in variable names.
+
+== How to fix it
+
+`Option Explicit` should be added to every individual source file.
+
+=== Code examples
+
+==== Noncompliant code example
+
+[source,vb6,diff-id=1,diff-type=noncompliant]
+----
+Sub DoSomething(First As String, Second As String)
+    Parameter = Fist        ' New local variable "Fist" is created and assigned to new local variable "Parameter" instead of "First" argument.
+    DoSomething(Parameter)
+    Parametr = Second       ' "Second" argument is assigned to newly created variable "Parametr" instead of intended "Parameter".
+    DoSomething(Parameter)  ' Value of "Parameter" is always Nothing
+End Sub
+----
+
+
+==== Compliant solution
+
+[source,vb6,diff-id=1,diff-type=compliant]
+----
+Option Explicit
+
+Sub DoSomething(First As String, Second As String)
+    Dim Parameter As String = First
+    DoSomething(Parameter)
+    Parameter = Second
+    DoSomething(Parameter)
+End Sub
+----