[llvm] [llvm][CodeGen] Add a new software pipeliner 'Window Scheduler' (PR #84443)

[Hua Tian via llvm-commits]

huaatian wrote:

> > @dtcxzyw hi，yingwei，looks like our multiple commits were not squashed together~
> 
> Do you mean the commit message?

yes，there are five commits here.
<img width="615" alt="image" src="https://github.com/llvm/llvm-project/assets/142874007/e27cecef-8326-43cd-be90-43c86e805bdc">


https://github.com/llvm/llvm-project/pull/84443