This factors the conversion logic to be independent from WebGL code,
allowing us to write unit tests for it that can run in CI (since WebGL
can't run in CI).
It's not correct to multiply the number of components by the number of
bytes, since compact formats such as 4_4_4_4 have 4 components but
_always_ stored in 2 bytes, not 8 if you were to do such a
multiplication.
Fixes textures on Google Maps having large blank stripes.
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
