AST printing: take more care to only escape 'Self' when needed.

Cleans up AST printing somewhat as well as providing slightly better
type-to-declaration mappings for annotated AST printing and indexing.

Swift SVN r32420

lib/AST/Decl.cpp

@@ -2049,6 +2049,14 @@ SourceRange GenericTypeParamDecl::getSourceRange() const {
   return SourceRange(getNameLoc(), endLoc);
 }
 
+bool GenericTypeParamDecl::isProtocolSelf() const {
+  if (!isImplicit()) return false;
+  auto dc = getDeclContext();
+  if (!dc->isProtocolOrProtocolExtensionContext()) return false;
+  return dc->getProtocolSelf() == this;
+}
+
+
 AssociatedTypeDecl::AssociatedTypeDecl(DeclContext *dc, SourceLoc keywordLoc,
                                        Identifier name, SourceLoc nameLoc,
                                        TypeLoc defaultDefinition)