Debugger: Rework type handlers to allow for custom selection.

TypeHandler:
- Add name field for presentation purposes. Adapt subclasses accordingly.

TypeHandlerRoster:
- Add methods to count and retrieve all type handlers for a given type,
  and adjust CreateValueNode to allow for passing in an explicit handler.
  Adjust callers accordingly.

VariablesViewState:
- Add helpers to store an explicitly chosen type handler for a node.

TypeHandlerMenuItem:
- ActionMenuItem subclass that takes care of reference management
  for its contained type handler.

VariablesView:
- Add context menu for choosing type handlers if applicable. Implement
  support for invoking said type handlers in a similar manner to explicit
  typecasts.
- Adjust saving/restoring the view state so that hidden nodes are taken
  into account as well. This is necessary since it may be the case that
  the handler had to be applied to the hidden child rather than the visible
  node (i.e. the BMessage handler when applied to a pointer to a BMessage).

All together, these changes allow choosing to switch between views of a type
when the Debugger has multiple handlers for it. For example, for BMessages
this allows switching between displaying the raw underlying structure vs
the decoded message content.

headers/private/debugger/value/TypeHandler.h

@@ -1,5 +1,6 @@
 /*
  * Copyright 2009, Ingo Weinhold, [email protected].
+ * Copyright 2018, Rene Gollent, [email protected].
  * Distributed under the terms of the MIT License.
  */
 #ifndef TYPE_HANDLER_H
@@ -18,7 +19,8 @@ class TypeHandler : public BReferenceable {
 public:
 	virtual						~TypeHandler();
 
-	virtual	float				SupportsType(Type* type) = 0;
+	virtual	const char*			Name() const = 0;
+	virtual	float				SupportsType(Type* type) const = 0;
 	virtual	status_t			CreateValueNode(ValueNodeChild* nodeChild,
 									Type* type, ValueNode*& _node) = 0;
 									// returns a reference

headers/private/debugger/value/TypeHandlerRoster.h

@@ -1,5 +1,6 @@
 /*
  * Copyright 2009, Ingo Weinhold, [email protected].
+ * Copyright 2018, Rene Gollent, [email protected].
  * Distributed under the terms of the MIT License.
  */
 #ifndef TYPE_HANDLER_ROSTER_H
@@ -31,11 +32,18 @@ public:
 			status_t			Init();
 			status_t			RegisterDefaultHandlers();
 
-			status_t			FindTypeHandler(ValueNodeChild* nodeChild,
+			int32				CountTypeHandlers(Type* type);
+			status_t			FindBestTypeHandler(ValueNodeChild* nodeChild,
 									Type* type, TypeHandler*& _handler);
 									// returns a reference
+			status_t			FindTypeHandlers(ValueNodeChild* nodeChild,
+									Type* type, TypeHandlerList*& _handlers);
+									// returns list of references
 			status_t			CreateValueNode(ValueNodeChild* nodeChild,
-									Type* type, ValueNode*& _node);
+									Type* type, TypeHandler* handler,
+									ValueNode*& _node);
+									// handler can be null if automatic
+									// search is desired.
 									// returns a reference
 
 			bool				RegisterHandler(TypeHandler* handler);