The existing `::unite_horizontally()` and `::unite_vertically()` tests
did not properly test the edge cases where left/top in the Rect were
updated, so they get re-arranged a bit.
This accurately reflects the spec it's implementing. This algorithm is
used in 5 spots in the spec but the old buggy behavior was never
triggered:
* In both ::extract() and ::clone_the_contents(), invocations to this
method are guarded by a check to see if the start node is the
inclusive ancestor of the end node, or vice versa - effectively
resulting in the inequality checks to be accidentally correct.
* In ::surround_contents(), we forego the usage of this algorithm as
stated in the spec, and instead use a correct and more optimized
version that simply compares the start and end nodes.
A lot of words to say: no functional changes :^)
Previously, it was assumed that nodes must share the same root, prior
to the calculation of their relative boundary point positions. This is
no longer the case, since `Selection.setBaseAndExtent()` now accepts
anchor and focus nodes that may be in different shadow trees.
Resulting in a massive rename across almost everywhere! Alongside the
namespace change, we now have the following names:
* JS::NonnullGCPtr -> GC::Ref
* JS::GCPtr -> GC::Ptr
* JS::HeapFunction -> GC::Function
* JS::CellImpl -> GC::Cell
* JS::Handle -> GC::Root
The main motivation behind this is to remove JS specifics of the Realm
from the implementation of the Heap.
As a side effect of this change, this is a bit nicer to read than the
previous approach, and in my opinion, also makes it a little more clear
that this method is specific to a JavaScript Realm.
