Refactor PIM/Common (splitting in files, adding helpers, adding brief

docs)

src/PIM/Common/Support/FileSystemUtils.hpp

@@ -0,0 +1,13 @@
+#pragma once
+
+#include <string>
+
+namespace onnx_mlir {
+
+/// Returns the directory that should hold PIM artifacts/debug dumps for the
+/// current compiler invocation.
+std::string getOutputDir();
+
+void createDirectory(const std::string& directory);
+
+} // namespace onnx_mlir