Expose ScalarizerPass options to C++ (not just commandline)

Context: I needed this for https://github.com/google/iree/pull/8474 .
I found that TSan instrumentation expects vector sizes to be <= 16,
and in my project (IREE) we have tests with higher vector sizes.
That left some test functions uninstrumented, resulting in crashes as
instrumented code called into them.

Differential Revision: https://reviews.llvm.org/D121182