LibJS: Implement the Temporal.Duration constructor

This also includes a stubbed Temporal.Duration.prototype.

Until we have re-implemented Temporal.PlainDate/ZonedDateTime, some of
Temporal.Duration.compare (and its invoked AOs) are left unimplemented.

Libraries/LibJS/Runtime/Temporal/AbstractOperations.h

@@ -14,9 +14,84 @@
 #include <LibJS/Runtime/Completion.h>
 #include <LibJS/Runtime/VM.h>
 #include <LibJS/Runtime/ValueInlines.h>
+#include <math.h>
 
 namespace JS::Temporal {
 
+// https://tc39.es/proposal-temporal/#sec-temporal-units
+enum class Unit {
+    Year,
+    Month,
+    Week,
+    Day,
+    Hour,
+    Minute,
+    Second,
+    Millisecond,
+    Microsecond,
+    Nanosecond,
+};
+StringView temporal_unit_to_string(Unit);
+
+// https://tc39.es/proposal-temporal/#sec-temporal-units
+enum class UnitCategory {
+    Date,
+    Time,
+};
+
+// https://tc39.es/proposal-temporal/#sec-temporal-units
+enum class UnitGroup {
+    Date,
+    Time,
+    DateTime,
+};
+
+struct Unset { };
+using RoundingIncrement = Variant<Unset, u64>;
+
+struct RelativeTo {
+    // FIXME: Make these objects represent their actual types when we re-implement them.
+    GC::Ptr<JS::Object> plain_relative_to; // [[PlainRelativeTo]]
+    GC::Ptr<JS::Object> zoned_relative_to; // [[ZonedRelativeTo]]
+};
+
+ThrowCompletionOr<RelativeTo> get_temporal_relative_to_option(VM&, Object const& options);
+bool is_calendar_unit(Unit);
+UnitCategory temporal_unit_category(Unit);
+ThrowCompletionOr<GC::Ref<Duration>> parse_temporal_duration_string(VM&, StringView iso_string);
+
+// 13.38 ToIntegerWithTruncation ( argument ), https://tc39.es/proposal-temporal/#sec-tointegerwithtruncation
+template<typename... Args>
+ThrowCompletionOr<double> to_integer_with_truncation(VM& vm, Value argument, ErrorType error_type, Args&&... args)
+{
+    // 1. Let number be ? ToNumber(argument).
+    auto number = TRY(argument.to_number(vm));
+
+    // 2. If number is NaN, +∞𝔽 or -∞𝔽, throw a RangeError exception.
+    if (number.is_nan() || number.is_infinity())
+        return vm.throw_completion<RangeError>(error_type, forward<Args>(args)...);
+
+    // 3. Return truncate(ℝ(number)).
+    return trunc(number.as_double());
+}
+
+// 13.38 ToIntegerWithTruncation ( argument ), https://tc39.es/proposal-temporal/#sec-tointegerwithtruncation
+// AD-HOC: We often need to use this AO when we have a parsed StringView. This overload allows callers to avoid creating
+//         a PrimitiveString for the primary definition.
+template<typename... Args>
+ThrowCompletionOr<double> to_integer_with_truncation(VM& vm, StringView argument, ErrorType error_type, Args&&... args)
+{
+    // 1. Let number be ? ToNumber(argument).
+    auto number = string_to_number(argument);
+
+    // 2. If number is NaN, +∞𝔽 or -∞𝔽, throw a RangeError exception.
+    if (isnan(number) || isinf(number))
+        return vm.throw_completion<RangeError>(error_type, forward<Args>(args)...);
+
+    // 3. Return truncate(ℝ(number)).
+    return trunc(number);
+}
+
 // 13.39 ToIntegerIfIntegral ( argument ), https://tc39.es/proposal-temporal/#sec-tointegerifintegral
 template<typename... Args>
 ThrowCompletionOr<double> to_integer_if_integral(VM& vm, Value argument, ErrorType error_type, Args&&... args)