CodeAssist: Use settable property for IAssistProposal::isFragile

Removes the need to create yet another subclass (for overriding a
virtual method) in some situations.

Change-Id: I55d70de60b4f8d127a175d996f797700c2f172a6
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@qt.io>

src/plugins/texteditor/codeassist/functionhintproposal.cpp

@@ -32,16 +32,13 @@ using namespace TextEditor;
 FunctionHintProposal::FunctionHintProposal(int cursorPos, IFunctionHintProposalModel *model)
     : IAssistProposal(cursorPos)
     , m_model(model)
-{}
+{
+    setFragile(true);
+}
 
 FunctionHintProposal::~FunctionHintProposal()
 {}
 
-bool FunctionHintProposal::isFragile() const
-{
-    return true;
-}
-
 IAssistProposalModel *FunctionHintProposal::model() const
 {
     return m_model;