LibJS: Replace comparisons of "0"_bigint with SignedBigInteger::is_zero

This just avoids creating UnsignedBigInteger's underlying vector.

Userland/Libraries/LibJS/Runtime/AbstractOperations.h

@@ -183,7 +183,7 @@ auto modulo(T x, U y) requires(IsArithmetic<T>, IsArithmetic<U>)
 
 auto modulo(Crypto::BigInteger auto const& x, Crypto::BigInteger auto const& y)
 {
-    VERIFY(y != "0"_bigint);
+    VERIFY(!y.is_zero());
     auto result = x.divided_by(y).remainder;
     if (result.is_negative())
         result = result.plus(y);

Userland/Libraries/LibJS/Runtime/Intl/NumberFormat.cpp

@@ -446,7 +446,7 @@ static ALWAYS_INLINE bool is_zero(Value number)
 {
     if (number.is_number())
         return number.as_double() == 0.0;
-    return number.as_bigint().big_integer() == Crypto::SignedBigInteger::create_from(0);
+    return number.as_bigint().big_integer().is_zero();
 }
 
 static ALWAYS_INLINE bool is_greater_than(Value number, i64 rhs)

Userland/Libraries/LibJS/Runtime/Temporal/Duration.cpp

@@ -1530,7 +1530,7 @@ ThrowCompletionOr<DurationRecord> adjust_rounded_duration_days(GlobalObject& glo
     i32 direction;
 
     // 3. If timeRemainderNs = 0, let direction be 0.
-    if (time_remainder_ns == "0"_bigint)
+    if (time_remainder_ns.is_zero())
         direction = 0;
     // 4. Else if timeRemainderNs < 0, let direction be -1.
     else if (time_remainder_ns.is_negative())

Userland/Libraries/LibJS/Runtime/Temporal/ZonedDateTime.cpp

@@ -452,7 +452,7 @@ ThrowCompletionOr<NanosecondsToDaysResult> nanoseconds_to_days(GlobalObject& glo
     auto day_length_ns = ns_per_day_bigint;
 
     // 2. If nanoseconds = 0, then
-    if (nanoseconds == "0"_bigint) {
+    if (nanoseconds.is_zero()) {
         // a. Return the Record { [[Days]]: 0, [[Nanoseconds]]: 0, [[DayLength]]: dayLengthNs }.
         return NanosecondsToDaysResult { .days = 0, .nanoseconds = "0"_sbigint, .day_length = day_length_ns.to_double() };
     }