[Scope map] A local property name is in scope within its own accessors.

While the use of a local property from within its own accessors is a
bit dubious, Swift 3 only warned on it, so model the existing lookup
behavior in the scope map.

include/swift/AST/Decl.h

@@ -1709,7 +1709,10 @@ public:
   void setInitContext(DeclContext *dc) { InitContext = dc; }
 
   /// Retrieve the source range covered by this pattern binding.
-  SourceRange getSourceRange() const;
+  ///
+  /// \param omitAccessors Whether the computation should omit the accessors
+  /// from the source range.
+  SourceRange getSourceRange(bool omitAccessors = false) const;
 };
 
 /// \brief This decl contains a pattern and optional initializer for a set