to_edge_transform_and_lower is broken when backend partitioners request aliased/mutable ops to be preserved

🐛 Describe the bug

When a backend partitioner asked for an alised or mutable op to be preserved, it runs into issues with run_decompositions() because those ops are added to a custom namespace EDGE_DO_NOT_DECOMP.

This runs into many issues during lowering because they are no longer aten ops, and PyTorch doesn't support aliasing on custom ops during functionalization / alias removing.

The ideal long term solution for to_edge_transform_and_lower is to:

1. First functionalize the graph, remove aliased ops, do type promotion, etc.
2. Ask partitioners for ops to preserve ops
3. Run decompositions

Today, step 1 happens inside of step 3 and after step 2. Since step 2 adds ops to the EDGE_DO_NOT_DECOMP, this creates many issues.

https://github.com/pytorch/executorch/pull/8776 has a short term fix.

Versions

Collecting environment information...
PyTorch version: 2.7.0.dev20250131
Is debug build: False
CUDA used to build PyTorch: None
ROCM used to build PyTorch: N/A

OS: macOS 15.3.1 (arm64)
GCC version: Could not collect
Clang version: 16.0.0 (clang-1600.0.26.3)
CMake version: version 3.31.4
Libc version: N/A

Python version: 3.10.16 (main, Dec 11 2024, 10:22:29) [Clang 14.0.6 ] (64-bit runtime)
Python platform: macOS-15.3.1-arm64-arm-64bit
Is CUDA available: False
CUDA runtime version: No CUDA
CUDA_MODULE_LOADING set to: N/A
GPU models and configuration: No CUDA
Nvidia driver version: No CUDA
cuDNN version: No CUDA
HIP runtime version: N/A
MIOpen runtime version: N/A
Is XNNPACK available: True

CPU:
Apple M1 Pro

Versions of relevant libraries:
[pip3] executorch==0.6.0a0+49d11b1
[pip3] executorchcoreml==0.0.1
[pip3] flake8==6.1.0
[pip3] flake8-breakpoint==1.1.0
[pip3] flake8-bugbear==24.4.26
[pip3] flake8-comprehensions==3.14.0
[pip3] flake8-plugin-utils==1.3.3
[pip3] flake8-pyi==23.5.0
[pip3] mypy==1.14.1
[pip3] mypy-extensions==1.0.0
[pip3] numpy==2.2.3
[pip3] torch==2.7.0.dev20250131
[pip3] torchao==0.8.0+git11333ba2
[pip3] torchaudio==2.6.0.dev20250131
[pip3] torchsr==1.0.4
[pip3] torchvision==0.22.0.dev20250131
[conda] executorch 0.6.0a0+49d11b1 pypi_0 pypi
[conda] executorchcoreml 0.0.1 pypi_0 pypi
[conda] numpy 2.2.3 pypi_0 pypi
[conda] torch 2.7.0.dev20250131 pypi_0 pypi
[conda] torchao 0.9.0+git04f3f03d pypi_0 pypi
[conda] torchaudio 2.6.0.dev20250131 pypi_0 pypi
[conda] torchfix 0.6.0 pypi_0 pypi
[conda] torchsr 1.0.4 pypi_0 pypi
[conda] torchvision 0.22.0.dev20250131 pypi_0 pypi

cc @JacobSzwejbka @angelayi