Update on "[devtool] make ETDumpGen use datasink"

This diff enables customized debug data pipeline by making ETDumpGen leverage user-provided datasink.

Details can be found in https://docs.google.com/document/d/1y_m32mKdj-OgLcLUz9TKhBW3PC3bBDYSBbeAH544EfM/edit?tab=t.0#heading=h.jlkcrurw482r

Differential Revision: [D69647096](https://our.internmc.facebook.com/intern/diff/D69647096/)

[ghstack-poisoned]

devtools/etdump/etdump_flatcc.cpp

@@ -630,7 +630,7 @@ size_t ETDumpGen::get_debug_buffer_size() const {
 }
 
 size_t ETDumpGen::get_data_sink_size() const {
-  ET_CHECK_MSG(data_sink_, "Must set data sink before checking its size\n");
+  ET_CHECK_MSG(data_sink_, "Must set data sink before checking its size");
   Result<size_t> ret = data_sink_->get_storage_size();
   ET_CHECK_MSG(
       ret.ok(),
@@ -640,7 +640,7 @@ size_t ETDumpGen::get_data_sink_size() const {
 }
 
 long ETDumpGen::write_tensor_or_raise_error(Tensor tensor) {
-  ET_CHECK_MSG(data_sink_, "Must set data sink before writing data\n");
+  ET_CHECK_MSG(data_sink_, "Must set data sink before writing data");
   Result<size_t> ret =
       data_sink_->write(tensor.const_data_ptr(), tensor.nbytes());
   ET_CHECK_MSG(