Add VB support.

src/EditorFeatures/VisualBasicTest/Structure/InterpolatedStringExpressionStructureTests.vb

+' Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
+
+Imports Microsoft.CodeAnalysis.Structure
+Imports Microsoft.CodeAnalysis.VisualBasic.Structure
+Imports Microsoft.CodeAnalysis.VisualBasic.Syntax
+
+Namespace Microsoft.CodeAnalysis.Editor.VisualBasic.UnitTests.Outlining
+    Public Class InterpolatedStringExpressionStructureTests
+        Inherits AbstractVisualBasicSyntaxNodeStructureProviderTests(Of InterpolatedStringExpressionSyntax)
+
+        Friend Overrides Function CreateProvider() As AbstractSyntaxStructureProvider
+            Return New InterpolatedStringExpressionStructureProvider()
+        End Function
+
+        <Fact, Trait(Traits.Feature, Traits.Features.Outlining)>
+        Public Async Function TestMultiLineStringLiteral() As Task
+            Const code = "
+Class C
+    Sub M()
+        Dim v =
+{|hint:{|textspan:$$$""
+{123}
+""|}|}
+    End Sub
+End Class
+"
+
+            Await VerifyBlockSpansAsync(code,
+                Region("textspan", "hint", "...", autoCollapse:=True))
+        End Function
+
+        <Fact, Trait(Traits.Feature, Traits.Features.Outlining)>
+        Public Async Function TestMissingOnIncompleteStringLiteral() As Task
+            Const code = "
+Class C
+    Sub M()
+        Dim v =
+$$$""
+    End Sub
+End Class
+"
+
+            Await VerifyNoBlockSpansAsync(code)
+        End Function
+    End Class
+End Namespace

src/Features/VisualBasic/Portable/Structure/Providers/InterpolatedStringExpressionStructureProvider.vb

+' Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
+
+Imports System.Threading
+Imports Microsoft.CodeAnalysis.Options
+Imports Microsoft.CodeAnalysis.PooledObjects
+Imports Microsoft.CodeAnalysis.Structure
+Imports Microsoft.CodeAnalysis.VisualBasic.Syntax
+
+Namespace Microsoft.CodeAnalysis.VisualBasic.Structure
+    Friend Class InterpolatedStringExpressionStructureProvider
+        Inherits AbstractSyntaxNodeStructureProvider(Of InterpolatedStringExpressionSyntax)
+
+        Protected Overrides Sub CollectBlockSpans(node As InterpolatedStringExpressionSyntax, spans As ArrayBuilder(Of BlockSpan), options As OptionSet, cancellationToken As CancellationToken)
+            If node.DollarSignDoubleQuoteToken.IsMissing OrElse
+               node.DoubleQuoteToken.IsMissing Then
+                Return
+            End If
+
+            spans.Add(New BlockSpan(
+                type:=BlockTypes.Expression,
+                isCollapsible:=True,
+                textSpan:=node.Span,
+                autoCollapse:=True,
+                isDefaultCollapsed:=False))
+        End Sub
+    End Class
+End Namespace

src/Features/VisualBasic/Portable/Structure/VisualBasicBlockStructureProvider.vb

@@ -80,6 +80,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Structure
             builder.Add(Of XmlElementSyntax, XmlExpressionStructureProvider)()
             builder.Add(Of XmlProcessingInstructionSyntax, XmlExpressionStructureProvider)()
             builder.Add(Of LiteralExpressionSyntax, StringLiteralExpressionStructureProvider)()
+            builder.Add(Of InterpolatedStringExpressionSyntax, InterpolatedStringExpressionStructureProvider)()
 
             Return builder.ToImmutable()
         End Function