Debugger: Minor tweak to DwarfType.

- When creating a derived type, adjust the name accordingly to indicate
  the additional qualifiers. Fixes a problem where casted type names would be
  displayed as their base type only, even if they included pointers or array
  subscripts.
Debugger: Fix type value display in VariablesView.

- When retrieving the type to display for a given model node, ask its
  underlying value node for its corresponding type rather than relying
  on the one initially stored in the model, as the latter can change
  as a result of typecasts.