[Static Runtime] Fold linear prepack ops (#85289)
Summary: Split `quantized_linear_unpacked_weight_v2` into `linear_prepack` and `quantized_linear` so that the prepacking operation may be eliminated by constant folding.
Test Plan:
Fixes a huge regression in an internal model:
```
Before
89.6141 ms. 99.0923%. fb::quantized_linear_unpacked_weight_v2 (12 nodes)
After
0.806852 ms. 53.5365%. quantized::linear (12 nodes, out variant)
(prepacking eliminated)
```
Differential Revision: D39622530
Pull Request resolved: https://github.com/pytorch/pytorch/pull/85289
Approved by: https://github.com/davidberard98
