Negate was incorrectly returning "== 0", a copy/paste from EqualsZero.
This patch corrects it to return "neg", matching the operator's actual
semantics and WebAssembly mnemonics (f32.neg, f64.neg).
Instead of returning whichever argument was NaN, return the canonical
NaN instead. The spec allows the old behavior:
"Following the recommendation that operators propagate NaN payloads
from their operands is permitted but not required."
But Chrome, Firefox and Safari do not propagate the operand payloads.
Fixes 448 WPT subtests in `wasm/core`.
Co-authored-by: Ali Mohammad Pur <ali.mpfard@gmail.com>
