[fx] Upstream the turbine FxImporter to torch-mlir. (#2681)

Changes made during upstreaming:

* Removed comments attributing some copied code back to torch-mlir
(since it is now repatriated).
* Re-organized imports.
* Inlined RefMapping/RefTracker and TypeSubclassMap from an external
utility module.
* Added FxImporter class comments.
* Updated stack trace extraction to be fail safe.
* Added an entry-point for `import_frozen_exported_program` which uses
the shiny new upstream `torch.export.export()` API (versus the
lower-level/older API that Turbine is presently using). This
necessitated a small FX rewrite to line external state management up
with current conventions.
* Adapted one of Turbine's importer tests to go with this initial
submission. Turbine unfortunately has a lot of more-integration-ey
tests, and I would like to extract those as more of unit tests of the
importer features and upstream them that way vs trying to copy directly.
For now, one overall test with the initial submission gets us moving.

I acknowledge that there are some code quality things that could be
improved in this submission: this was authored over the course of many
months (and often via some trial and error). I would like to keep it
relatively converged with the downstream for the next few steps while
getting the test suite upstreamed. And then it will be easier to take a
hygienic pass through the code.

Including co-authors for contributors in the git log of the original
repository.

Co-authored-by: Ean Garvey <[email protected]>
Co-authored-by: Avinash Sharma <[email protected]>
Co-authored-by: Arham Khan <[email protected]>
Co-authored-by: brucekimrokcmu <[email protected]>
Co-authored-by: saienduri <[email protected]>

Author: 6 people

python/CMakeLists.txt

@@ -35,6 +35,7 @@ declare_mlir_python_sources(TorchMLIRPythonSources.Importers
   ROOT_DIR "${TORCH_MLIR_PYTHON_ROOT_DIR}"
   ADD_TO_PARENT TorchMLIRPythonSources
   SOURCES
+    extras/fx_importer.py
     extras/onnx_importer.py
 )