Fixup of extraction.

Author: michaelnebel

csharp/extractor/Semmle.Extraction.CSharp/CodeAnalysisExtensions/SymbolExtensions.cs

@@ -652,8 +652,23 @@ public static bool IsPublicOrProtected(this ISymbol symbol) =>
         /// <summary>
         /// Returns true if the given symbol should be extracted in this context.
         /// </summary>
-        public static bool ShouldExtractSymbol(this ISymbol symbol) =>
-            symbol.Locations.Any(x => !x.IsInMetadata) || symbol.IsPublicOrProtected();
+        public static bool ShouldExtractSymbol(this ISymbol symbol)
+        {
+            // Extract all source symbols and public/protected metadata symbols.
+            if (symbol.Locations.Any(x => !x.IsInMetadata) || symbol.IsPublicOrProtected())
+            {
+                return true;
+            }
+            if (symbol is IMethodSymbol method)
+            {
+                return method.ExplicitInterfaceImplementations.Any(m => m.ContainingType.DeclaredAccessibility == Accessibility.Public);
+            }
+            if (symbol is IPropertySymbol property)
+            {
+                return property.ExplicitInterfaceImplementations.Any(m => m.ContainingType.DeclaredAccessibility == Accessibility.Public);
+            }
+            return false;
+        }
 
         /// <summary>
         /// Returns the symbols that should be extracted in the given context.