vulkan: fuse mul_mat+add and mul_mat_id+add_id (#16868)

* vulkan: fuse mul_mat+add and mul_mat_id+add_id

The fusion is only applied for the mat-vec mul paths.

* Apply suggestions from code review

Co-authored-by: Sigbjørn Skjæret <[email protected]>

* fix 32b build

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Co-authored-by: Sigbjørn Skjæret <[email protected]>

Author: jeffbolznv