[mlir][StandardToSPIRV] Add support for lowering uitofp to SPIR-V

- Extend spirv::ConstantOp::getZero/One to handle float, vector of int, and vector of float.
- Refactor ZeroExtendI1Pattern to use getZero/One methods.
- Add one more test for lowering std.zexti which extends vector<4xi1> to vector<4xi64>.

Reviewed By: antiagainst

Differential Revision: https://reviews.llvm.org/D95120