Recommit "[RISCV] Make the operand order for RISCVISD::FSL(W)/FSR(W) match the...

Recommit "[RISCV] Make the operand order for RISCVISD::FSL(W)/FSR(W) match the instruction register numbering."

This reverts the revert commit e3283857.

Accidental demanded bits change has been removed. The demanded bits
code itself was remove in a pre-commit since it isn't tested.

Original commit message:
Previous we used the fshl/fshr operand ordering for simplicity. This
made things confusing when D117468 proposed adding intrinsics for
the instructions. We can't just use the generic funnel shifting
intrinsics because fsl/fsr have different functionality that should
be exposed to software.

Now we use rs1, rs3, rs2/shamt order which matches the instruction
printing order and the order used in this intrinsic header
https://github.com/riscv/riscv-bitmanip/blob/main-history/cproofs/rvintrin.h