Fix VB Module Sub New

Members of a Module are implicitly Shared.  Hence a Sub New is really a
static constructor and hence can't have a modifier.

closes #84

Author: jaredpar

src/Microsoft.DotNet.CodeFormatting.Tests/Rules/ExplicitVisibilityRuleTests.cs

@@ -825,6 +825,28 @@ End Sub
                 Verify(text, expected, runFormatter: false, languageName: LanguageNames.VisualBasic);
             }
 
+            /// <summary>
+            /// Members of a Module are implicitly Shared hence New here is a static ctor and cannot have
+            /// any visibility modifiers.
+            /// </summary>
+            [Fact]
+            public void ConstructorOnModules()
+            {
+                var text = @"
+Module M
+    Sub New()
+    End Sub
+End Module";
+
+                var expected = @"
+Friend Module M
+    Sub New()
+    End Sub
+End Module";
+
+                Verify(text, expected, runFormatter: false, languageName: LanguageNames.VisualBasic);
+            }
+
             [Fact]
             public void InterfaceMembers()
             {

src/Microsoft.DotNet.CodeFormatting/Rules/ExplicitVisibilityRule.VisualBasic.cs

@@ -21,6 +21,7 @@ private sealed class VisualBasicVisibilityRewriter : VisualBasicSyntaxRewriter
             private readonly Document _document;
             private readonly CancellationToken _cancellationToken;
             private SemanticModel _semanticModel;
+            private bool _inModule;
 
             internal VisualBasicVisibilityRewriter(Document document, CancellationToken cancellationToken)
             {
@@ -69,7 +70,17 @@ public override SyntaxNode VisitInterfaceBlock(InterfaceBlockSyntax originalNode
 
             public override SyntaxNode VisitModuleBlock(ModuleBlockSyntax node)
             {
-                node = (ModuleBlockSyntax)base.VisitModuleBlock(node);
+                var savedInModule = _inModule;
+                try
+                {
+                    _inModule = true;
+                    node = (ModuleBlockSyntax)base.VisitModuleBlock(node);
+                }
+                finally
+                {
+                    _inModule = savedInModule;
+                }
+
                 var begin = (ModuleStatementSyntax)EnsureVisibility(
                     node.ModuleStatement, 
                     node.ModuleStatement.ModuleKeyword,
@@ -110,7 +121,7 @@ public override SyntaxNode VisitMethodStatement(MethodStatementSyntax node)
 
             public override SyntaxNode VisitSubNewStatement(SubNewStatementSyntax node)
             {
-                if (node.Modifiers.Any(x => x.IsKind(SyntaxKind.SharedKeyword)))
+                if (node.Modifiers.Any(x => x.IsKind(SyntaxKind.SharedKeyword)) || _inModule)
                 {
                     return node;
                 }