gemma2: add sliding window mask (#8227)

* gemma2: add sliding window mask

* fix data_swa uninitialized

* better naming

* add co-author

Co-authored-by: Arlo Phoenix <arlo-phoenix@users.noreply.github.com>

* replace list with single tensor

* update

* llama : minor styling

* convert : add sanity check for query_pre_attn_scalar

* fix small typo in README

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Co-authored-by: Arlo Phoenix <arlo-phoenix@users.noreply.github.com>
Co-authored-by: Georgi Gerganov <ggerganov@gmail.com>