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

docs)

src/PIM/Common/IR/EntryPointUtils.hpp

@@ -0,0 +1,13 @@
+#pragma once
+
+#include "mlir/Dialect/Func/IR/FuncOps.h"
+#include "mlir/IR/BuiltinOps.h"
+
+namespace onnx_mlir {
+
+/// Resolves the function the PIM pipeline should treat as its entry point.
+/// Prefers ONNX entry-point metadata, then `main_graph`, then the only
+/// non-external function if the module is otherwise unambiguous.
+llvm::FailureOr<mlir::func::FuncOp> getPimEntryFunc(mlir::ModuleOp moduleOp);
+
+} // namespace onnx_mlir