Revert "Use std::optional"

[metascroy]

Reverts #12707

This causes 1000s of internal CI failures, e.g.,

error: no template named 'optional' in namespace 'torch::executor'; did you mean simply 'optional'?
using optional = torch::executor::optional;
^~~~~~~~~~~~~~~~~~~~~~~~~
optional
note: 'optional' declared here
using ::executorch::aten::optional;

[pytorch-bot]

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⏳ No Failures, 12 Pending

As of commit ece021b with merge base 149e23d ():
💚 Looks good so far! There are no failures yet. 💚

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[JacobSzwejbka]

cc @cyyever I think the root cause of the failures is what I mentioned on your follow up diff of we cant just remove the name "torch::executor::optional" you will need to leave that exposed as an alias for std::optional

[larryliu0820]

cc @cyyever I think the root cause of the failures is what I mentioned on your follow up diff of we cant just remove the name "torch::executor::optional" you will need to leave that exposed as an alias for std::optional

I think you just need to add this line:

#include <executorch/runtime/core/portable_type/optional.h> // @manual

To runtime/core/exec_aten/exec_aten.h