This revision adds a
```
FlatAffineValueConstraints(ValueRange ivs, ValueRange lbs, ValueRange ubs)
```
method and use it in hoist padding.
Differential Revision: https://reviews.llvm.org/D110427
This revision extracts padding hoisting in a new file and cleans it up in prevision of future improvements and extensions.
Differential Revision: https://reviews.llvm.org/D110414