[WebNN EP] Support local attention feature for GQA (#26565)
### Description
<!-- Describe your changes. -->
Support the `local_window_size` attribute in **GroupQueryAttention**
Operator, which is designed for sliding window attention and may
influence the attention mask pattern.
For local window size not equal to -1, new attention mask pattern will
be created as follows for applying sliding window.
```
condition_1 (old attn_mask) ---> CumSum (axis=3, exclusive=true, reversed=true)
| |
| Lesser <--- local_window_size
| |
LogicalAnd <----------------- condition_2
|
new attn_mask
```
### Motivation and Context
<!-- - Why is this change required? What problem does it solve?
- If it fixes an open issue, please link to the issue here. -->
