abstract aways file2rwmapped construction to lower visibility

solanaceae/ngc_ft1_sha1/file_constructor.cpp

@@ -0,0 +1,8 @@
+#include "./file_constructor.hpp"
+
+#include "./file_rw_mapped.hpp"
+
+std::unique_ptr<File2I> construct_file2_rw_mapped(std::string_view file_path, int64_t file_size) {
+	return std::make_unique<File2RWMapped>(file_path, file_size);
+}
+