data: indexer processes

* TaskBuildIndex starts seperate indexer processes and communicates via shared memory
* indexer processes get restarted if they fail
* indexer processes are killed when the app closes or crashes
* added utility class SharedMemory to allocate and access shared memory, providing basic data structures
* added SharedMemoryGarbageCollector for keeping track of running instances and cleaning up shared memory in case of a crash
* show errors for source files that crashed during indexing
* added basic exception handling to task scheduling
* added option to turn off processes and use threads in preferences, but still use shared memory

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src/lib_gui/qt/window/QtIndexingDialog.cpp

@@ -153,7 +153,7 @@ void QtIndexingDialog::setupIndexing()
 
 void QtIndexingDialog::setupReport(
 	size_t indexedFileCount, size_t totalIndexedFileCount, size_t completedFileCount, size_t totalFileCount,
-	float time)
+	float time, bool interrupted)
 {
 	QBoxLayout* layout = createLayout();
 
@@ -182,7 +182,7 @@ void QtIndexingDialog::setupReport(
 
 	m_sizeHint = QSize(400, 280);
 
-	if (indexedFileCount != totalIndexedFileCount)
+	if (interrupted)
 	{
 		updateTitle("Interrupted Indexing");
 	}