Fix tensor name/type disagreement on multi-output nodes

[psiddh]

Summary:
define_tensor decides twice whether the tensor it is defining is a graph
output: once for the tensor name (get_tensor_name -> is_graph_output, which
prefixes output_) and once for the tensor type (get_tensor_type ->
is_graph_output, which returns QNN_TENSOR_TYPE_APP_READ). Since
is_graph_output gained an output_index parameter, only the type path has been
passing it:

output_index = wrapper_idx if tensor_source_node is target_build_node else None

The name path still passed the raw wrapper_idx. wrapper_idx only indexes a
node's own outputs when the tensor being defined belongs to that node; builders
also use it to key scratch tensors sourced from some other node (see
op_scatter_elements), where it carries no output meaning. For a non-owner
multi-output source node at a partition boundary the two paths therefore answer
differently: the tensor gets an output_-prefixed name while its type stays
NATIVE, or gets APP_READ without the name the runtime expects. QNN graph
construction then fails, and because it depends on partitioning order it fails
intermittently -- this is the flake in test-qnn-testsuite-linux /
test-backend-linux (qnn, models).

This computes output_index once and feeds it to both paths, so naming and
typing can no longer disagree. get_tensor_name takes output_index as a new
optional argument that defaults to None, preserving the behavior of any
external caller that does not pass it.

The fbcode/ and xplat/ copies of node_visitor.py are byte-identical
mirrors, so both are updated.

Authored with AI assistance (Claude Code).

Differential Revision: D118035167

[pytorch-bot]

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❌ 2 New Failures, 1 Unrelated Failure

As of commit f9e248a with merge base c27baa8 ():

NEW FAILURES - The following jobs have failed:

• Cadence Build & Test / hifi-build / hifi4 (gh)
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• Cadence Build & Test / vision-build / vision (gh)
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BROKEN TRUNK - The following job failed but were present on the merge base:

👉 Rebase onto the `viable/strict` branch to avoid these failures

• pull / test-qnn-testsuite-linux / test-backend-linux (qnn, models) / linux-job (gh) (trunk failure)

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