[executorch][native] Add Value + index-arena ids to the in-memory IR

[SS-JIA]

Stack from ghstack (oldest at bottom):

• [executorch][native] Add deserializer bridge (Program -> Method) #22105
• [executorch][native] Add Method + ValueRole to the in-memory IR #22104
• [executorch][native] Add Graph index arena to the in-memory IR #22103
• [executorch][native] Add Node to the in-memory IR #22102
• [executorch][native] Add Argument tagged union to the in-memory IR #22101
• -> [executorch][native] Add Value + index-arena ids to the in-memory IR #22100
• [executorch][native] Add Scalar value type to the in-memory IR #22099
• [executorch][native] Add TensorMeta + ScalarType in-memory IR types #22098
• [executorch][native] Add native runtime Program reader + Graphviz visualizer #22097
• [executorch][native] Add native_executor test harness #22096

Next in-memory IR types for the native runtime, under
backends/native/runtime/graph/:

• Ids.h — NodeRef / ValueRef, plain int32_t index-arena aliases (ET-VK
  vkapi style) plus kInvalid and a valid() helper. NodeRef indexes
  Graph.nodes; ValueRef indexes Graph.values.
• Value (Value.{h,cpp}) — one SSA value (dataflow edge): a tagged union
  (ValueKind = None / Tensor / Scalar / List) over per-kind members, plus
  def-use wiring (producer / consumers), a storage alias_of, and an open
  attrs (std::any) scratch map. Construct via the tensor / scalar /
  list / none factories; read via typed accessors that throw on a kind
  mismatch. A List holds ValueRefs to its element values (an arena
  grouping), so nesting is via the arena and there is no recursive value type;
  the AOT deserializer builds only Tensor / Scalar / None.

Pure std — no ExecuTorch and no flatbuffers dependency. Mirrored into both the
fbcode/ and xplat/ trees to match the native backend layout.

Authored with Claude Code.

Differential Revision: D114396769

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/22100

• 📄 Preview Python docs built from this PR

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

✅ You can merge normally! (1 Unrelated Failure)

As of commit 195db91 with merge base 9a2d135 ():

FLAKY - The following job failed but was likely due to flakiness present on trunk:

• pull / test-qnn-testsuite-linux / test-backend-linux (qnn, models) / linux-job (gh) (matched linux rule in flaky-rules.json)
  The runner has received a shutdown signal. This can happen when the runner service is stopped, or a manually started runner is canceled.

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

[github-actions]

This PR needs a release notes: label

If your change should be included in the release notes (i.e. would users of this library care about this change?), please use a label starting with release notes:. This helps us keep track and include your important work in the next release notes.

To add a label, you can comment to pytorchbot, for example
@pytorchbot label "release notes: none"

For more information, see
https://github.com/pytorch/pytorch/wiki/PyTorch-AutoLabel-Bot#why-categorize-for-release-notes-and-how-does-it-work.