add ScratchX compatibility layer

[kokofixcomputers]

Extensions that are using ScratchExtensions instead of Scratch.extension are not working example:

ScratchExtensions.register('ChatGPT', descriptor, ext);

It works normally on turbowarp using their custom extension loader.

[SimonShiki]

Seems it's a Turbowarp's ScratchX compatibility layer stuff, Are there still amounts of Scratch extensions still using it?

[kokofixcomputers]

Seems it's a Turbowarp's ScratchX compatibility layer stuff, Are there still amounts of Scratch extensions still using it?

In a list of extensions, I still see 4-5 that are still using it...