Add addcmul, lerp to fuser, enable scalar->float specialization in symbolic script (#18081)
Summary:
This PR did two things:
1. Enable scalar->float specialization in symbolic script, so AD formula that contains scalar in the schema, should write `float` instead.
2. add addcmul, lerp to AD and fuser.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/18081
Differential Revision: D14490493
Pulled By: wanchaol
fbshipit-source-id: b3b86d960d5f051b30733bc908b19786111cdaa4
