[mlir][Vector] Add a VectorUnrollInterface and expose UnrollVectorPattern.

The UnrollVectorPattern is can be used in a programmable fashion by:
```
OwningRewritePatternList patterns;
    patterns.insert<UnrollVectorPattern<AddFOp>>(ArrayRef<int64_t>{2, 2}, ctx);
    patterns.insert<UnrollVectorPattern<vector::ContractionOp>>(
        ArrayRef<int64_t>{2, 2, 2}, ctx);
    ...
    applyPatternsAndFoldGreedily(getFunction(), patterns);
```

Differential revision: https://reviews.llvm.org/D83064