[mlir][SliceAnalysis] Add an options object to forward and backward slice.

Add an options object to allow control of the slice computation (for
both forward and backward slice). This makes the ABI stable, and also
allows avoiding an assert that makes the slice analysis unusable for
operations with multiple blocks.

Reviewed By: hanchung, nicolasvasilache

Differential Revision: https://reviews.llvm.org/D151520