Issue 5258 - Implement Filter::As<>() method to make working with filters easier from C++ code

compiled/filter/Filter.cpp

Index: compiled/filter/Filter.cpp
===================================================================
--- a/compiled/filter/Filter.cpp
+++ b/compiled/filter/Filter.cpp
@@ -117,35 +117,35 @@ Filter* Filter::FromText(DependentString
   {
     knownFilter->second->AddRef();
     return knownFilter->second;
   }
 
   FilterPtr filter;
   switch (type)
   {
-    case Filter::Type::COMMENT:
+    case CommentFilter::classType:
       filter = FilterPtr(new CommentFilter(text), false);
       break;
-    case Filter::Type::INVALID:
+    case InvalidFilter::classType:
       filter = FilterPtr(new InvalidFilter(text, error), false);
       break;
-    case Filter::Type::BLOCKING:
+    case BlockingFilter::classType:
       filter = FilterPtr(new BlockingFilter(text, data.regexp), false);
       break;
-    case Filter::Type::WHITELIST:
+    case WhitelistFilter::classType:
       filter = FilterPtr(new WhitelistFilter(text, data.regexp), false);
       break;
-    case Filter::Type::ELEMHIDE:
+    case ElemHideFilter::classType:
       filter = FilterPtr(new ElemHideFilter(text, data.elemhide), false);
       break;
-    case Filter::Type::ELEMHIDEEXCEPTION:
+    case ElemHideException::classType:
       filter = FilterPtr(new ElemHideException(text, data.elemhide), false);
       break;
-    case Filter::Type::ELEMHIDEEMULATION:
+    case ElemHideEmulationFilter::classType:
       filter = FilterPtr(new ElemHideEmulationFilter(text, data.elemhide), false);
       if (static_cast<ElemHideEmulationFilter*>(filter.get())->IsGeneric())
         filter = FilterPtr(new InvalidFilter(text, u"filter_elemhideemulation_nodomain"_str), false);
       break;
     default:
       // This should never happen but just in case
       return nullptr;
   }