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/element/QtCodeFileTitleButton.cpp

@@ -66,9 +66,12 @@ void QtCodeFileTitleButton::setIsComplete(bool isComplete)
 
 	if (!isComplete)
 	{
+		FilePath hatchingFilePath(ResourcePaths::getGuiPath().str() + "code_view/images/pattern_" +
+			ColorScheme::getInstance()->getColor("code/file/title/hatching") + ".png"
+		);
+
 		setStyleSheet((
-			"background-image: url(" + ResourcePaths::getGuiPath().str() + "code_view/images/pattern_" +
-			ColorScheme::getInstance()->getColor("code/file/title/hatching") + ".png);"
+			"background-image: url(" + hatchingFilePath.str() + ");"
 		).c_str());
 	}
 	else