Make dumpers pass on more size information initially, namely the
various Q<>Pointers. Introduce enum for those special template types
whose size does not vary with the arguments (Q<>Pointer,
std::allocators...) to make it more easily extensible.
Pass on some common QMapNode<> sizes as well.
Introduce an expression cache to the common QtDumperHelper
class and make dumpers pass some common expression values
(value offsets of common QMapNode<> incarnations).
Make CDBDumperHelper use the expression cache.
Extend dumper tester.