Implement Portable bucketize

[Gallinator]

Fixes #20270

Summary

Add portable scalar and tensor bucketize operator, based on the PyTorch implementation.
Key differences from the PyTorch implementation:

• Implemented only bucketize, no searchsorted
• Boundaries tensor size is not checked against output type, as SizesType is an int32_t and must be 1D
• In the original implementation the input scalar is wrapped into a tensor, here two sets of functions are used instead
• Supports both NHWC and NCHW as it is a pointwise kernel and there is no sorter argument. This avoids creating contiguous tensors

Release notes: ops & kernels

Test plan

C++ tests are extensive and include failure and edge cases tests.
Python tests compare the output of an exported module to the PyTorch implementation only for normal and edge cases, similar to #15893.

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/20287

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⚠️ 12 Awaiting Approval

As of commit 3057642 with merge base 0378fc4 ():

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[Gallinator]

@pytorchbot label "release notes: ops & kernels"