No functional changes - we can still very easily get to the global
object via `Realm::global_object()`. This is in preparation of moving
the intrinsics to the realm and no longer having to pass a global
object when allocating any object.
In a few (now, and many more in subsequent commits) places we get a
realm using `GlobalObject::associated_realm()`, this is intended to be
temporary. For example, create() functions will later receive the same
treatment and are passed a realm instead of a global object.
This commit adds an initial implementation (without any real locale
support) of Collator Compare Functions, as well as the matching
CompareStrings AO. These two are used to implement the ECMA402 version
of String.localeCompare() and Int.Collator.compare().
