[ImportVerilog] add real literal support, refine real type, and add real format support

[chenbo-again]

This PR is aimed to support systemverilog real, shortreal, realtime, and there conversion and operation.

One thing I'm not so sure about is that

class BinaryOpBase<string mnemonic, list<Trait> traits = []> :
    MooreOp<mnemonic, traits # [Pure, SameOperandsAndResultType]> {
  let arguments = (ins SimpleBitVectorType:$lhs, SimpleBitVectorType:$rhs);
  let results = (outs SimpleBitVectorType:$result);
  let assemblyFormat = [{
    $lhs `,` $rhs attr-dict `:` type($result)
  }];
}

why this opbase just support SimpleBitVectorType? is there any shortcoming to just convert it to a UnpackedType? I also want to use this OpBase support float point operation.

[hailongSun2000]

Maybe we can extend its argument and result type, like AnyStaticArrayType defined in MooreTypes.td.

[hailongSun2000]

Could you add some test cases? And thanks for your work on this 😄.