LibJS: Add a way of constructing PropertyName with values above 2**32-1

This is often needed in ArrayPrototype when getting items with indices
above 2**32-1 is possible since length is at most 2**53-1.
This also fixes a number of these cases in ArrayPrototype where the type
was not big enough to hold the potential values.

Userland/Libraries/LibJS/Runtime/ArrayPrototype.cpp

@@ -737,14 +737,15 @@ JS_DEFINE_NATIVE_FUNCTION(ArrayPrototype::slice)
         return {};
 
     size_t index = 0;
+    size_t k = actual_start;
 
-    while (actual_start < final) {
+    while (k < final) {
-        bool present = this_object->has_property((u32)actual_start);
+        bool present = this_object->has_property(k);
         if (vm.exception())
             return {};
 
         if (present) {
-            auto value = this_object->get((u32)actual_start);
+            auto value = this_object->get(k);
             if (vm.exception())
                 return {};
 
@@ -753,7 +754,7 @@ JS_DEFINE_NATIVE_FUNCTION(ArrayPrototype::slice)
                 return {};
         }
 
-        ++actual_start;
+        ++k;
         ++index;
     }
 
@@ -801,18 +802,18 @@ JS_DEFINE_NATIVE_FUNCTION(ArrayPrototype::index_of)
     if (Value(n).is_negative_infinity())
         n = 0;
 
-    u32 k;
+    size_t k;
 
     // 8. If n ≥ 0, then
     if (n >= 0) {
         // a. Let k be n.
-        k = (u32)n;
+        k = (size_t)n;
     }
     // 9. Else,
     else {
         // a. Let k be len + n.
         // b. If k < 0, set k to 0.
-        k = max((i32)length + (i32)n, 0);
+        k = max(length + n, 0);
     }
 
     // 10. Repeat, while k < len,
@@ -1036,7 +1037,7 @@ JS_DEFINE_NATIVE_FUNCTION(ArrayPrototype::reduce_right)
                 return {};
 
             // ii. Set accumulator to ? Call(callbackfn, undefined, « accumulator, kValue, 𝔽(k), O »).
-            accumulator = vm.call(callback_function.as_function(), js_undefined(), accumulator, k_value, Value((i32)k), object);
+            accumulator = vm.call(callback_function.as_function(), js_undefined(), accumulator, k_value, Value((size_t)k), object);
             if (vm.exception())
                 return {};
         }
@@ -1311,17 +1312,17 @@ JS_DEFINE_NATIVE_FUNCTION(ArrayPrototype::last_index_of)
     if (Value(n).is_negative_infinity())
         return Value(-1);
 
-    i32 k;
+    ssize_t k;
 
     // 6. If n ≥ 0, then
     if (n >= 0) {
         // a. Let k be min(n, len - 1).
-        k = min((i32)n, (i32)length - 1);
+        k = min(n, (double)length - 1);
     }
     // 7. Else,
     else {
         //  a. Let k be len + n.
-        k = (i32)length + (i32)n;
+        k = (double)length + n;
     }
 
     // 8. Repeat, while k ≥ 0,
@@ -1345,7 +1346,7 @@ JS_DEFINE_NATIVE_FUNCTION(ArrayPrototype::last_index_of)
 
             // iii. If same is true, return 𝔽(k).
             if (same)
-                return Value(k);
+                return Value((size_t)k);
         }
 
         // c. Set k to k - 1.
@@ -1361,7 +1362,7 @@ JS_DEFINE_NATIVE_FUNCTION(ArrayPrototype::includes)
     auto* this_object = vm.this_value(global_object).to_object(global_object);
     if (!this_object)
         return {};
-    i32 length = length_of_array_like(global_object, *this_object);
+    auto length = length_of_array_like(global_object, *this_object);
     if (vm.exception())
         return {};
     if (length == 0)

Userland/Libraries/LibJS/Runtime/PropertyName.h

@@ -43,14 +43,21 @@ public:
 
     template<Integral T>
     PropertyName(T index)
-        : m_type(Type::Number)
-        , m_number(index)
     {
         // FIXME: Replace this with requires(IsUnsigned<T>)?
         //        Needs changes in various places using `int` (but not actually being in the negative range)
         VERIFY(index >= 0);
-        if constexpr (NumericLimits<T>::max() >= NumericLimits<u32>::max())
+        if constexpr (NumericLimits<T>::max() >= NumericLimits<u32>::max()) {
-            VERIFY(index < NumericLimits<u32>::max());
+            if (index >= NumericLimits<u32>::max()) {
+                m_string = String::number(index);
+                m_type = Type::String;
+                m_string_may_be_number = false;
+                return;
+            }
+        }
+
+        m_type = Type::Number;
+        m_number = index;
     }
 
     PropertyName(char const* chars)