Add a Clang NATVIS visualizer for StringLiteral

Author: AaronBallman

clang/utils/ClangVisualizers/clang.natvis

@@ -1000,8 +1000,15 @@ For later versions of Visual Studio, no setup is required-->
     </Expand>
   </Type>
   <Type Name="clang::Expr">
+    <DisplayString Condition="StmtBits.sClass==clang::Stmt::StmtClass::StringLiteralClass" IncludeView="poly">{*(clang::StringLiteral *)this}</DisplayString>
     <DisplayString>Expression of class {(clang::Stmt::StmtClass)StmtBits.sClass,en} and type {TR,view(cpp)}</DisplayString>
   </Type>
+  <Type Name="clang::StringLiteral">
+    <Expand>
+      <Item Name="Length">*(unsigned *)(((clang::StringLiteral *)this)+1)</Item>
+      <Item Name="Data" Condition="StringLiteralBits.NumConcatenated==1">(const char *)(((clang::StringLiteral *)this)+1)+4+4,[*(unsigned *)(((clang::StringLiteral *)this)+1)]s8</Item>
+    </Expand>
+  </Type>
   <Type Name="clang::DeclAccessPair">
     <DisplayString IncludeView="access" Condition="(Ptr&amp;Mask) == clang::AS_public">public</DisplayString>
     <DisplayString IncludeView="access" Condition="(Ptr&amp;Mask) == clang::AS_protected">protected</DisplayString>