Editor: delete assist interface in lsp/clangd support

The complete memory management in the code assistant needs an overhaul.
For now just delete or at least track the assist interface with scoped
pointers.

Fixes: QTCREATORBUG-28408
Change-Id: I0bd4cfaa36a660b6fd5bb467af3b13414ed76e63
Reviewed-by: Jarek Kobus <jaroslaw.kobus@qt.io>
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>

src/plugins/clangcodemodel/clangdfollowsymbol.cpp

@@ -12,6 +12,7 @@
 #include <languageclient/languageclientsymbolsupport.h>
 #include <languageserverprotocol/lsptypes.h>
 #include <languageserverprotocol/jsonrpcmessages.h>
+#include <texteditor/codeassist/assistinterface.h>
 #include <texteditor/codeassist/iassistprocessor.h>
 #include <texteditor/codeassist/iassistprovider.h>
 #include <texteditor/textdocument.h>
@@ -41,8 +42,9 @@ public:
     void resetData(bool resetFollowSymbolData);
 
 private:
-    IAssistProposal *perform(const AssistInterface *) override
+    IAssistProposal *perform(const AssistInterface *interface) override
     {
+        delete interface;
         return nullptr;
     }