[Tracker] Expanded BF16 Support

Tracking issue for expanding BF16 support. See https://github.com/google/XNNPACK/issues/9599 for initial discussion.

* [ ] Support bf16 <-> fp32 convert ops.
* [x] Scalar: https://github.com/google/XNNPACK/pull/9727
* [x] Neon (w/o FEAT_BF16): https://github.com/google/XNNPACK/pull/9922
* [x] Neon (w/ FEAT_BF16): https://github.com/google/XNNPACK/pull/9922
* [ ] SSE/AVX (target TBD)
* [x] AVX512: https://github.com/google/XNNPACK/pull/10023
* [x] AVX512_BF16: https://github.com/google/XNNPACK/pull/10023
* [ ] Support bf16 <-> qs/qu8 convert ops.
* [ ] Scalar
* [x] Minmax: https://github.com/google/XNNPACK/pull/9858
* [x] bf16->qs8: https://github.com/google/XNNPACK/pull/9984
* [ ] Neon (w/o FEAT_BF16)
* [x] Minmax: https://github.com/google/XNNPACK/pull/10024
* [ ] Neon (w/ FEAT_BF16)
* [ ] SSE/AVX (target TBD)
* [ ] AVX512_BF16
* [x] Operator wiring: https://github.com/google/XNNPACK/pull/10022
* [ ] Update src/qs8-gemm/ to add qd8-bf16 variants.
* [x] Scalar: https://github.com/google/XNNPACK/pull/9960
* [ ] SSE2
* [ ] AVX2
* [ ] AVX512
* [ ] AVX512_BF16
* [ ] Neon (w/o FEAT_BF16)
* [ ] Neon (w/ FEAT_BF16)
* [ ] https://github.com/google/XNNPACK/pull/10631
* [ ] Wire up bf16 in the subgraph layer for supported operators.
* [ ] Support subgraph rewrite (bf16 -> fp32) for ops without native bf16 support.
* [ ] https://github.com/google/XNNPACK/pull/10629