LibJS: Add ECMA-262 section/title/URL comments almost everywhere

As mentioned on Discord earlier, we'll add these to all new functions
going forward - this is the backfill. Reasons:

- It makes you look at the spec, implementing based on MDN or V8
  behavior is a no-go
- It makes finding the various functions that are non-compliant easier,
  in the future everything should either have such a comment or, if it's
  not from the spec at all, a comment explaining why that is the case
- It makes it easier to check whether a certain abstract operation is
  implemented in LibJS, not all of them use the same name as the spec.
  E.g. RejectPromise() is Promise::reject()
- It makes it easier to reason about vm.arguments(), e.g. when the
  function has a rest parameter
- It makes it easier to see whether a certain function is from a
  proposal or Annex B

Also:

- Add arguments to all functions and abstract operations that already
  had a comment
- Fix some outdated section numbers
- Replace some ecma-international.org URLs with tc39.es

Userland/Libraries/LibJS/Runtime/BigIntConstructor.cpp

@@ -23,7 +23,10 @@ void BigIntConstructor::initialize(GlobalObject& global_object)
 {
     auto& vm = this->vm();
     NativeFunction::initialize(global_object);
+
+    // 21.2.2.3 BigInt.prototype, https://tc39.es/ecma262/#sec-bigint.prototype
     define_property(vm.names.prototype, global_object.bigint_prototype(), 0);
+
     define_property(vm.names.length, Value(1), Attribute::Configurable);
 
     // TODO: Implement these functions below and uncomment this.
@@ -36,6 +39,7 @@ BigIntConstructor::~BigIntConstructor()
 {
 }
 
+// 21.2.1.1 BigInt ( value ), https://tc39.es/ecma262/#sec-bigint-constructor-number-value
 Value BigIntConstructor::call()
 {
     auto primitive = vm().argument(0).to_primitive(global_object(), Value::PreferredType::Number);
@@ -54,17 +58,20 @@ Value BigIntConstructor::call()
     return bigint;
 }
 
+// 21.2.1.1 BigInt ( value ), https://tc39.es/ecma262/#sec-bigint-constructor-number-value
 Value BigIntConstructor::construct(Function&)
 {
     vm().throw_exception<TypeError>(global_object(), ErrorType::NotAConstructor, "BigInt");
     return {};
 }
 
+// 21.2.2.1 BigInt.asIntN ( bits, bigint ), https://tc39.es/ecma262/#sec-bigint.asintn
 JS_DEFINE_NATIVE_FUNCTION(BigIntConstructor::as_int_n)
 {
     TODO();
 }
 
+// 21.2.2.2 BigInt.asUintN ( bits, bigint ), https://tc39.es/ecma262/#sec-bigint.asuintn
 JS_DEFINE_NATIVE_FUNCTION(BigIntConstructor::as_uint_n)
 {
     TODO();