Handle RNN activation parameters safely (#31675)
This pull request prevents out-of-bounds reads of RNN activation
parameters while preserving ONNX-spec-legal attribute lists.
**RNN activation parameter handling:**
* Reuses the shared `rnn::detail::ActivationFuncs` normalization already
used by ORT's LSTM and GRU kernels.
* Consumes `activation_alpha` and `activation_beta` values only for
activation functions that require them.
* Applies activation-specific ONNX defaults when a required value is
absent, including `LeakyRelu`, `HardSigmoid`, and `Elu` defaults.
* Safely accepts empty, shorter, and longer parameter lists without
indexing those lists by direction.
**Unit test coverage:**
* Verifies mixed activations consume only the required alpha and beta
values.
* Verifies empty parameter attributes use activation-specific defaults.
* Verifies a missing `LeakyRelu` alpha uses the ONNX default of `0.01`.
* Verifies extra alpha and beta entries are safely ignored.
The tests run explicitly on the CPU execution provider and no longer
contain an unrelated DML skip.
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Co-authored-by: Copilot <223556219@users.noreply.github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
