Detect float point type earlier in BGV pipeline

[ZenithalHourlyRate]

Currently the detection of float point type and the warning for it is in --secret-to-bgv. However, earlier pass like --validate-noise assumes input in BGV style, and float point input to it will segfault.

As we put the scheme flag in the pipeline like --mlir-to-bgv, we know the scheme parameter from the begining so we could reject it earlier.

[ai-mannamalai]

It seems like the segfault-ing pass should run validation as well no ? O(n) cost to explore ops, regions and types and declare kaput

[j2kun]

Agreed, I believe I commented elsewhere that I think we would benefit from some early passes that just walk the IR and do early validation on things like types.