ParserHelper: reorganized usesContextProperly() to make the logic more clear.
ParserHelper: use getParameterSlotCount() in usesContextProperly().
ParserHelper: usesContextProperly() now takes a MethodNode, instead of 3 separate arguments extracted from the method node.
SnippetParser, ProcessorParser: adjusted to pass a MethodNode into usesContextProperly().