Support for Dtye Selective Build from Dictionary API in OSS (cmake)

[BujSet]

Summary

When attempting to build minimal binary size with only a select number of operators and dtypes, it's advantageous to simply specify only the needed selections at compile time. This PR allows one to specify a JSON formatted string to select operators and dtypes to be included in the final binary. An example is also provided.

Test plan

This feature was tested with the added example in examples/selective_build/test_selective_build.sh which now has a function named test_cmake_select_ops_in_dict(). This function exemplifies the usage of the newly added dictionary API.

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/12873

• 📄 Preview Python docs built from this PR

Note: Links to docs will display an error until the docs builds have been completed.

❗ 1 Active SEVs

There are 1 currently active SEVs. If your PR is affected, please view them below:

• Failing to create ec2 instances -> lots of queueing

❌ 1 New Failure, 81 Pending

As of commit 6ba45eb with merge base 8651d31 ():

NEW FAILURE - The following job has failed:

• pull / unittest-editable / macos / macos-job (gh)
  backends/xnnpack/test/ops/test_conv1d.py::TestConv1d::test_qs8_conv1d_batchnorm_seq

This comment was automatically generated by Dr. CI and updates every 15 minutes.

[BujSet]

@pytorchbot label "release notes: none"

[lucylq]

Could we add a link to the supported dtype strings, e.g. https://github.com/pytorch/executorch/blame/0211a0346455f5b1ce445c2bdf6fce89a9aa04c9/shim_et/xplat/executorch/codegen/codegen.bzl#L51

^ actually I think this list is too broad and not all supported in ET 😅

[BujSet]

I think there are actually only 8 dtypes that are supported and tested. I remember seeing a list of them somewhere in the code base, will note them here.