Keep canonical form of Yul code at all times.

libyul/optimiser/BlockFlattener.cpp

@@ -43,3 +43,15 @@ void BlockFlattener::operator()(Block& _block)
 		}
 	);
 }
+
+void BlockFlattener::run(OptimiserStepContext&, Block& _ast)
+{
+	BlockFlattener flattener;
+	for (auto& statement: _ast.statements)
+		if (auto* block = get_if<Block>(&statement))
+			flattener(*block);
+		else if (auto* function = get_if<FunctionDefinition>(&statement))
+			flattener(function->body);
+		else
+			yulAssert(false, "BlockFlattener requires the FunctionGrouper.");
+}