[CUDA] Update benchmark_mha.py to capture debug info to identify sdpa kernel (#21804)
Use debug info to identify sdpa kernel actually used, and show it in the
output of benchmark_mha.py. This updated benchmark script was used to
get the benchmark results in
https://github.com/microsoft/onnxruntime/pull/21629.
(1) Change the output format of debug info to output like SdpaKernel=*
(2) Add a step to capture stdout from onnxruntime session, and use
regular expression to parse SdpaKernel=* from the captured text.
Other minor changes:
(1) Set different default repeats during benchmark: 100 for CPU; and
10000 for CUDA.
(2) Fix PrintTensorByDims used in console dumper: if it is not enabled,
do not dump tensor.
(3) Update some comments
### Motivation and Context
Sometime, we will use fallback for a sdpa_kernel. It could confuse user
unless we can tell exact kernel is used in benchmark.