Repository: pytorch
Issue: [Export] aten::_transformer_encoder_layer_fwd is not core aten and has no decomposition.
Labels: module: nn,oncall: export

### 🐛 Describe the bug

The following script;

```
import torch
layer = torch.nn.TransformerEncoderLayer(4, 2, 1, batch_first=True)
layer.eval()
input = torch.randn(4, 4, 4)

exported = torch.export.export(layer, (input, ))
exported.run_decompositions()
for node in exported.graph_module.graph.nodes:
    if node.op == 'call_function':
        print(node.target)
        print(node.target.tags)
```

Gives:
```
(torch310) hanq@hanq-compile-2:/mnt/hanq/git/qihqi/pytorch/xla$ python test.py
aten._transformer_encoder_layer_fwd.default
[<Tag.pt2_compliant_tag: 8>]
```

### Versions

Collecting environment information...

Socket(s):                       2
Stepping:                        0
BogoMIPS:                        6100.00
Flags:                           fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx mmxext fxsr_opt pdpe1gb rdtscp lm constant_tsc rep_good nopl nonstop_tsc cpuid extd_apicid tsc_known_freq pni pclmulqdq monitor ssse3 fma cx16 pcid sse4_1 sse4_2 movbe popcnt aes xsave avx f16c rdrand hypervisor lahf_lm cmp_legacy cr8_legacy abm sse4a misalignsse 3dnowprefetch osvw topoext invpcid_single ssbd ibrs ibpb stibp vmmcall fsgsbase tsc_adjust bmi1 avx2 smep bmi2 erms invpcid rdseed adx smap clflushopt clwb sha_ni xsaveopt xsavec xgetbv1 clzero xsaveerptr arat npt nrip_save umip vaes vpclmulqdq rdpid fsrm
Hypervisor vendor:               KVM
Virtualization type:             full
L1d cache:                       1.8 MiB (56 instances)
L1i cache:                       1.8 MiB (56 instances)
L2 cache:                        28 MiB (56 instances)
L3 cache:                        448 MiB (14 instances)
NUMA node(s):                    2
NUMA node0 CPU(s):               0-27,56-83
NUMA node1 CPU(s):               28-55,84-111
Vulnerability Itlb multihit:     Not affected
Vulnerability L1tf:              Not affected
Vulnerability Mds:               Not affected
Vulnerability Meltdown:          Not affected
Vulnerability Mmio stale data:   Not affected
Vulnerability Retbleed:          Not affected
Vulnerability Spec store bypass: Mitigation; Speculative Store Bypass disabled via prctl
Vulnerability Spectre v1:        Mitigation; usercopy/swapgs barriers and __user pointer sanitization
Vulnerability Spectre v2:        Mitigation; Retpolines, IBPB conditional, IBRS_FW, STIBP conditional, RSB filling, PBRSB-eIBRS Not affected
[pip3] mypy-extensions==1.0.0
[pip3] numpy==1.26.1
[pip3] onnx==1.13.1
[pip3] onnxruntime==1.15.1
[pip3] torch==2.3.0a0+gitb4ef59f
[pip3] torch-xla==2.2.0+gita80c1e7
[pip3] torchaudio==2.2.0.dev20231010+cpu
[pip3] torchdata==0.7.0
[pip3] torchsr==1.0.4
[pip3] torchtext==0.16.0
[pip3] torchvision==0.17.0.dev20231010+cpu
[pip3] triton==2.1.0
[conda] blas                      1.0                         mkl
[conda] executorch                0.1.0                    pypi_0    pypi
[conda] mkl                       2023.1.0         h6d00ec8_46342
[conda] mkl-include               2023.2.0                 pypi_0    pypi
[conda] mkl-service               2.4.0           py310h5eee18b_1
[conda] mkl_fft                   1.3.6           py310h1128e8f_1
[conda] mkl_random                1.2.2           py310h1128e8f_1
[conda] numpy                     1.26.1                   pypi_0    pypi
[conda] torch                     2.3.0a0+gitb4ef59f          pypi_0    pypi
[conda] torch-xla                 2.2.0+gita80c1e7           dev_0    <develop>
[conda] torchaudio                2.2.0.dev20231010+cpu          pypi_0    pypi
[conda] torchdata                 0.7.0                    pypi_0    pypi
[conda] torchsr                   1.0.4                    pypi_0    pypi
[conda] torchtext                 0.16.0                   pypi_0    pypi
[conda] torchvision               0.17.0.dev20231010+cpu          pypi_0    pypi
[conda] triton                    2.1.0                    pypi_0    pypi

cc @albanD @mruberry @jbschlosser @walterddr @mikaylagawarecki @avikchaudhuri @gmagogsfm @zhxchen17 @tugsbayasgalan @angelayi @suo @ydwu4 @penguinwu @bhosmer @cpuhrsch @erichan1 @drisspg