CodeAssist: Move base position to interface.

Every proposal needs to have a base postion.
Move it to the base class to reduce duplicated code.

Change-Id: I0b1b8282dfe955d251646661f755bf9f585fbad1
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/texteditor/codeassist/iassistproposal.cpp

@@ -59,7 +59,8 @@ using namespace TextEditor;
     \sa IAssistProposalWidget, IAssistModel
 */
 
-IAssistProposal::IAssistProposal()
+IAssistProposal::IAssistProposal(int basePosition)
+    : m_basePosition(basePosition)
 {}
 
 IAssistProposal::~IAssistProposal()
@@ -79,6 +80,11 @@ IAssistProposal::~IAssistProposal()
     Returns the position from which this proposal starts.
 */
 
+int IAssistProposal::basePosition() const
+{
+    return m_basePosition;
+}
+
 /*!
     \fn bool TextEditor::IAssistProposal::isCorrective() const