TextEditor: Introduce AssistProposalItemInterface

For unit test we need to break every dependency to the TextEditor
Widget etc.. With an abstract interface we can implement it in clang
without relying on unwanted dependencies. It makes it also easier to
compute the values deferred.

Change-Id: I1b313a1625f4e80bd324ab4bf1a7c4f6b690abe9
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@theqtcompany.com>

src/plugins/texteditor/codeassist/assistproposalitem.cpp

@@ -60,19 +60,12 @@ namespace TextEditor {
     This is the place to implement the actual application of the item.
 */
 
-AssistProposalItem::AssistProposalItem()
-    : m_order(0)
-{}
-
-AssistProposalItem::~AssistProposalItem()
-{}
-
 void AssistProposalItem::setIcon(const QIcon &icon)
 {
     m_icon = icon;
 }
 
-const QIcon &AssistProposalItem::icon() const
+QIcon AssistProposalItem::icon() const
 {
     return m_icon;
 }
@@ -92,7 +85,7 @@ void AssistProposalItem::setDetail(const QString &detail)
     m_detail = detail;
 }
 
-const QString &AssistProposalItem::detail() const
+QString AssistProposalItem::detail() const
 {
     return m_detail;
 }
@@ -107,14 +100,19 @@ const QVariant &AssistProposalItem::data() const
     return m_data;
 }
 
-int AssistProposalItem::order() const
+bool AssistProposalItem::isSnippet() const
 {
-    return m_order;
+    return data().canConvert<QString>();
 }
 
-void AssistProposalItem::setOrder(int order)
+bool AssistProposalItem::isValid() const
 {
-    m_order = order;
+    return m_data.isValid();
+}
+
+quint64 AssistProposalItem::hash() const
+{
+    return 0;
 }
 
 bool AssistProposalItem::implicitlyApplies() const