When this is true, we have to vertically flip TexImageSource provided
images before uploading them.
Fixes several graphical glitches on Google Maps.
Fixes globe being upside down on Shopify's homepage.
Likely fixes more websites.
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
