[mlir][scf] Add parallelLoopUnrollByFactors() (#163806)
- In the SCF Utils, add the `parallelLoopUnrollByFactors()` function
to unroll scf::ParallelOp loops according to the specified unroll factors
- Add a test pass "TestParallelLoopUnrolling" and the related LIT test
- Expose `mlir::parallelLoopUnrollByFactors()`, `mlir::generateUnrolledLoop()`,
and `mlir::scf::computeUbMinusLb()` functions in the
mlir/Dialect/SCF/Utils/Utils.h header to make them available
to other passes.
- In `mlir::generateUnrolledLoop()`, add also an optional
`IRMapping *clonedToSrcOpsMap` argument to map the new cloned
operations to their original ones.
In the function body, change the default `AnnotateFn` type to
`static const` to silence potential warnings about dangling references
when a function_ref is assigned to a variable with automatic storage.
Signed-off-by: Fabrizio Indirli <Fabrizio.Indirli@arm.com>
