CodeAssist: Support asynchronous processing without threads

This is required for the CodemodelBackendIPC integration in the
ClangCodeModelPlugin. Since the heavy calculation happens in a separate
process, we only need to send appropriate requests and receive results
for a working completion. However, the CodeAssist API does not fit here
since it only provides means of caculating the results in the main
thread or a worker thread. We can't use the worker thread approach since
that would lead to threading issues regarding QLocalSocket in
CodemodelBackendIPC.

IAssistProcessor::setAsyncProposalAvailable() will hand the results
back to CodeAssist in order to display them.

Change-Id: I496192560fb406ec40fa8bcb7904f7a03d2eef50
Reviewed-by: David Schulz <david.schulz@theqtcompany.com>

src/plugins/texteditor/codeassist/iassistprocessor.cpp

@@ -47,6 +47,18 @@ IAssistProcessor::IAssistProcessor()
 IAssistProcessor::~IAssistProcessor()
 {}
 
+void IAssistProcessor::setAsyncProposalAvailable(IAssistProposal *proposal)
+{
+    if (m_asyncCompletionsAvailableHandler)
+        m_asyncCompletionsAvailableHandler(proposal);
+}
+
+void IAssistProcessor::setAsyncCompletionAvailableHandler(
+        const IAssistProcessor::AsyncCompletionsAvailableHandler &finalizer)
+{
+    m_asyncCompletionsAvailableHandler = finalizer;
+}
+
 /*!
     \fn IAssistProposal *TextEditor::IAssistProcessor::perform(const AssistInterface *interface)