[CUDA] FusedMHARunnerFP16v2 thread-safe (#21420)
### Description
- [x] Rewrite FusedMHARunnerFP16v2 to make it thread-safe.
- [x] Add multi-threading tests
Previously, the kernel parameters params is stored as a member of mha
runner, which means that different threads might change the params at
the same time and impacts the other threads.
For example, if batch_size and seq_len was changed by another thread to
larger values in setup(...), buffer overrun might happen in run(...)
because a kernel could read/write memory out of range of allocated
buffers.
In new implementation, I change the api and remove mutable member
variables to make it thread safe. Below is summary of change:
Before:
```
class FusedMHARunnerFP16v2::mhaImpl {
void setup(int seq_len, int batch_size) {
// change scalar params
}
void run(input, output) {
// change params for input and output pointers
// launch kernel using params
}
Fused_multihead_attention_params_v2 params; // mutable, not thread-safe
}
```
After:
```
class FusedMHARunnerFP16v2::FmhaImpl {
void setup(int seq_len, int batch_size, Fused_multihead_attention_params_v2& params) {
// change params
}
void run(params, input, output) {
// change params with input and output pointers
// launch kernel using params
}
}
```
### Motivation and Context
https://github.com/microsoft/onnxruntime/issues/18854
https://github.com/microsoft/onnxruntime/issues/21413
