nir: Add more modulus and remainder opcodes

nir: Add more modulus and remainder opcodes

SPIR-V makes a distinction between "modulus" and "remainder" for both
floating-point and signed integer variants.  The difference is primarily
one of which source they take their sign from.  The "remainder" opcode for
integers is equivalent to the C/C++ "%" operation while the "modulus"
opcode is more mathematically correct (at least for an unsigned divisor).
This commit adds corresponding opcodes to NIR.