GDNative: Use VariantWriter for the API JSON generator
GDNative: Use VariantWriter for the API JSON generator

Instead of the String representation, which can be finicky to work with.
VariantWriter is more robust since changes to it affects the whole
system thus it's changed less often and it's never ambiguous.

akien-mga/godot,guilhermefelipecgs/godot,Valentactive/godot,josempans/godot,vkbsb/godot,sanikoyes/godot,honix/godot,honix/godot,guilhermefelipecgs/godot,sanikoyes/godot,Valentactive/godot,akien-mga/godot,DmitriySalnikov/godot,josempans/godot,Zylann/godot,Valentactive/godot,pkowal1982/godot,josempans/godot,josempans/godot,honix/godot,pkowal1982/godot,BastiaanOlij/godot,sanikoyes/godot,firefly2442/godot,Valentactive/godot,Shockblast/godot,BastiaanOlij/godot,godotengine/godot,Shockblast/godot,vnen/godot,ZuBsPaCe/godot,BastiaanOlij/godot,vkbsb/godot,vkbsb/godot,akien-mga/godot,sanikoyes/godot,Faless/godot,pkowal1982/godot,BastiaanOlij/godot,DmitriySalnikov/godot,ZuBsPaCe/godot,Shockblast/godot,Valentactive/godot,vnen/godot,guilhermefelipecgs/godot,akien-mga/godot,pkowal1982/godot,Shockblast/godot,vnen/godot,honix/godot,guilhermefelipecgs/godot,Faless/godot,godotengine/godot,Zylann/godot,godotengine/godot,godotengine/godot,pkowal1982/godot,vkbsb/godot,josempans/godot,josempans/godot,Zylann/godot,sanikoyes/godot,BastiaanOlij/godot,Faless/godot,Faless/godot,ZuBsPaCe/godot,Shockblast/godot,ZuBsPaCe/godot,Valentactive/godot,vkbsb/godot,guilhermefelipecgs/godot,akien-mga/godot,Faless/godot,firefly2442/godot,Faless/godot,ZuBsPaCe/godot,pkowal1982/godot,Zylann/godot,godotengine/godot,firefly2442/godot,firefly2442/godot,ZuBsPaCe/godot,sanikoyes/godot,Shockblast/godot,honix/godot,Faless/godot,BastiaanOlij/godot,vnen/godot,vnen/godot,vkbsb/godot,firefly2442/godot,guilhermefelipecgs/godot,akien-mga/godot,firefly2442/godot,Zylann/godot,guilhermefelipecgs/godot,Valentactive/godot,ZuBsPaCe/godot,sanikoyes/godot,josempans/godot,DmitriySalnikov/godot,BastiaanOlij/godot,godotengine/godot,DmitriySalnikov/godot,pkowal1982/godot,BastiaanOlij/godot,ZuBsPaCe/godot,vkbsb/godot,Zylann/godot,honix/godot,firefly2442/godot,akien-mga/godot,Valentactive/godot,DmitriySalnikov/godot,guilhermefelipecgs/godot,Faless/godot,josempans/godot,firefly2442/godot,vnen/godot,Shockblast/godot,akien-mga/godot,godotengine/godot,vkbsb/godot,vnen/godot,sanikoyes/godot,Zylann/godot,DmitriySalnikov/godot,Zylann/godot,Shockblast/godot,pkowal1982/godot,vnen/godot,godotengine/godot,DmitriySalnikov/godot