Rewrite `=== NaN` ⇒ `isNaN`

Convert comparisons to NaN (e.g., x == NaN) to use isNaN (e.g., isNaN(x)).

In JavaScript, NaN is a special value of Number type. It’s used to represent any of the not-a-number values represented by the double-precision 64-bit format as specified by the IEEE Standard for Binary Floating-Point Arithmetic.

NaN is unique in JavaScript by not being equal to anything, including itself, so it does not make sense to compare to it.

grit apply prefer_is_nan

if (foo == NaN) {
}

if (isNaN(foo)) {
}

if (foo === NaN) {
}

if (isNaN(foo)) {
}

if (foo != NaN) {
}

if (!isNaN(foo)) {
}

if (foo !== NaN) {
}

if (!isNaN(foo)) {
}

var x = NaN;