Add VirtualTable AST production.

Author: khuey

src/ast.rs

@@ -7413,7 +7413,9 @@ where
         match *self {
             SpecialName::VirtualTable(ref ty) => {
                 write!(ctx, "{{vtable(")?;
+                ctx.push_demangle_node(DemangleNodeType::VirtualTable);
                 ty.demangle(ctx, scope)?;
+                ctx.pop_demangle_node();
                 write!(ctx, ")}}")?;
                 Ok(())
             }

src/lib.rs

@@ -249,6 +249,8 @@ pub enum DemangleNodeType {
     DataMemberPrefix,
     /// Entering a <nested-name> production
     NestedName,
+    /// Entering a <special-name> production that is a vtable.
+    VirtualTable,
 }
 
 /// Sink for demangled text that reports syntactic structure.