[coreml] delegate multiple outputs (#88345)
Summary:
https://www.internalfb.com/code/fbsource/[c0e4da0b5c7fff3b4e31e4611033c30cabdc6aef]/fbcode/caffe2/torch/csrc/jit/backends/backend_detail.cpp?lines=268-276
seems like the torchscript addition of
`$unpack, = self.__backend.execute( ... `
the comma after unpack forces the result of execute to have only one item. So for this fix now when the size of the outputs > 1, execute returns a List List of outputs (basically put the outputs in another list before putting it into the list we return)
```
[[output1, output2, output3, ...]]
```
instead of
```
[output1, output2, output3, ...]
```
Do we want to fix this in backend_detail? Or should we make the change in our delegate to accomadate the torchscript? Proposing this q here. Requesting cccclai, kimishpatel for approval here
Test Plan: unblocked models for chengxiangyin and models in pytorch playground all passing unit tests
Reviewed By: kimishpatel, cccclai
Differential Revision: D40328684
Pull Request resolved: https://github.com/pytorch/pytorch/pull/88345
Approved by: https://github.com/jmdetloff, https://github.com/Skylion007
