[x64] Fix AVX-512 VECTOR_DENORMFLUSH merge-masking & FpRangeSign values

Copy src1 into dest before the masked vrangeps so that unmasked lanes
(normal/inf/NaN values) are preserved via merge-masking. Previously,
when the register allocator assigned different physical registers for
dest and src1, unmasked lanes would retain stale values from dest.

Tested with Intel SDE and AVX-512 cpu to verify.

Also shift unused FpRangeSign constants into bits [3:2] of the vrangeps
immediate, matching the Intel encoding. Only one used in the code was 0
so it was already correct by accident but using the others in the future
would produce incorrect results.

src/xenia/cpu/backend/x64/x64_util.h

@@ -47,10 +47,10 @@ constexpr uint8_t AbsMax = 0b11;  // Larger absolute value
 };  // namespace FpRangeSelect
 
 namespace FpRangeSign {
-constexpr uint8_t OperandA = 0b00;  // Copy sign of operand A
-constexpr uint8_t Preserve = 0b01;  // Leave sign as is
-constexpr uint8_t Positive = 0b10;  // Set Positive
-constexpr uint8_t Negative = 0b11;  // Set Negative
+constexpr uint8_t OperandA = 0b0000;  // Copy sign of operand A
+constexpr uint8_t Preserve = 0b0100;  // Leave sign as is
+constexpr uint8_t Positive = 0b1000;  // Set Positive
+constexpr uint8_t Negative = 0b1100;  // Set Negative
 };  // namespace FpRangeSign
 
 }  // namespace x64