mark abstract functions as such

Author: lostmsu

src/Analysis/Engine/Impl/Analyzer/FunctionAnalysisUnit.cs

@@ -109,17 +109,21 @@ private bool ProcessAbstractDecorators(IAnalysisSet decorator) {
                 switch (d.Name) {
                     case "abstractmethod":
                         res = true;
+                        Function.IsAbstract = true;
                         break;
                     case "abstractstaticmethod":
                         Function.IsStatic = true;
+                        Function.IsAbstract = true;
                         res = true;
                         break;
                     case "abstractclassmethod":
                         Function.IsClassMethod = true;
+                        Function.IsAbstract = true;
                         res = true;
                         break;
                     case "abstractproperty":
                         Function.IsProperty = true;
+                        Function.IsAbstract = true;
                         res = true;
                         break;
                 }

src/Analysis/Engine/Impl/Values/Definitions/IFunctionInfo.cs

@@ -23,6 +23,7 @@ public interface IFunctionInfo: IAnalysisValue {
         bool IsClassMethod { get; }
         bool IsProperty { get; }
         bool IsClosure { get; }
+        bool IsAbstract { get; }
         IPythonProjectEntry ProjectEntry { get; }
     }
 }

src/Analysis/Engine/Impl/Values/FunctionInfo.cs

@@ -84,6 +84,7 @@ private static bool CanBeClosure(PythonAnalyzer state, IPythonProjectEntry entry
         public bool IsStatic { get; set; }
         public bool IsClassMethod { get; set; }
         public bool IsProperty { get; set; }
+        public bool IsAbstract { get; internal set; }
         public bool IsClosure => _callsWithClosure != null;
 
         public override IAnalysisSet Call(Node node, AnalysisUnit unit, IAnalysisSet[] args, NameExpression[] keywordArgNames) {