[IDE/SourceKit] New SourceKit request for filtered method list

`source.request.conformingmethods` is a new SourceKit request which
receives a source position and a list of protocol namses, returns a list
of methods whose return type conforms to the requested protocols.

rdar://problem/44699573

tools/SourceKit/lib/SwiftLang/SwiftLangSupport.h

@@ -306,6 +306,13 @@ public:
     return CCCache;
   }
 
+  /// Copy a memory buffer inserting '0' at the position of \c origBuf.
+  // TODO: Share with code completion.
+  static std::unique_ptr<llvm::MemoryBuffer>
+  makeCodeCompletionMemoryBuffer(const llvm::MemoryBuffer *origBuf,
+                                 unsigned &Offset,
+                                 const std::string bufferIdentifier);
+
   static SourceKit::UIdent getUIDForDecl(const swift::Decl *D,
                                          bool IsRef = false);
   static SourceKit::UIdent getUIDForExtensionOfDecl(const swift::Decl *D);
@@ -381,6 +388,14 @@ public:
   static void
   printFullyAnnotatedGenericReq(const swift::GenericSignature *Sig,
                                 llvm::raw_ostream &OS);
+
+  /// Print 'description' or 'sourcetext' the given \p VD to \p OS. If
+  /// \p usePlaceholder is \c true, call argument positions are substituted with
+  /// a typed editor placeholders which is suitable for 'sourcetext'.
+  static void
+  printMemberDeclDescription(const swift::ValueDecl *VD, swift::Type baseTy,
+                             bool usePlaceholder, llvm::raw_ostream &OS);
+
   /// Tries to resolve the path to the real file-system path. If it fails it
   /// returns the original path;
   static std::string resolvePathSymlinks(StringRef FilePath);
@@ -528,6 +543,11 @@ public:
                                 ArrayRef<const char *> Args,
                                 TypeContextInfoConsumer &Consumer) override;
 
+  void getConformingMethodList(llvm::MemoryBuffer *inputBuf, unsigned Offset,
+                               ArrayRef<const char *> Args,
+                               ArrayRef<const char *> ExpectedTypes,
+                               ConformingMethodListConsumer &Consumer) override;
+
   void getStatistics(StatisticsReceiver) override;
 
 private: