[RISCV] Fix crash with fptosi.sat/fptoui.sat intrinsics on RV64. Add test cases.

Add PromoteIntOp_FP_TO_XINT_SAT to type legalize the bit width
operand from i32 to i64 for RV64.

Add test cases for the saturating intrinsics for half/float/double
and i32/i64. CodeGen is definitely not optimal. We can probably
make use of the native behavior of fcvt instructions in many cases.

Fixes PR50083