[WebNN] Fix bug in RotaryEmbedding (#24516)
This PR fixes incorrect input/output shape, according to [DML EP's
implementation](https://github.com/microsoft/onnxruntime/blob/main/onnxruntime/core/providers/dml/DmlExecutionProvider/src/Operators/DmlOperatorRotaryEmbedding.cpp#L142C47-L142C94),
we should ensure the input shape to be [batch_size, sequence_length,
num_heads, head_size].
