Fix long / Variant conversion for javascript platform

[maiself]

I was getting errors about ambiguous conversions from size_t to Variant when building code to wasm. I think this should be fine for all platforms, but I was only able to test these three: linux x86-64, mingw-w64, and emscripten.

[Faless]

I'm not sure I understand the changes. Can you provide an example of the failing code? Godot sources seems to do something similar, but only for iphone (not javascript).

[aaronfranke]

No response for 2 years and there are conflicts, closing.

If there is a problem with Variant, it should be fixed on the engine side first, and synced here.