Allow preload to accept a const string.
Allow preload to accept a const string.

In preload() parsing this code will lookup the identifier in the local
constant database. If the identifier corresponds to a string constant
it is used as the path for preload().

Currently this does not work for global constants, only constants
declared in the same class as the preload is happening. We can implement
a full fix too. Maybe we can use this PR to discuss the possibilities.

This (partially) fixes #6798

Paulloz/godot,josempans/godot,pkowal1982/godot,godotengine/godot,vnen/godot,pkowal1982/godot,ageazrael/godot,ficoos/godot,guilhermefelipecgs/godot,okamstudio/godot,tomreyn/godot,Faless/godot,Brickcaster/godot,mcanders/godot,ex/godot,Paulloz/godot,ZuBsPaCe/godot,exabon/godot,Valentactive/godot,Zylann/godot,Shockblast/godot,josempans/godot,vkbsb/godot,firefly2442/godot,ZuBsPaCe/godot,groud/godot,Max-Might/godot,Brickcaster/godot,jejung/godot,Valentactive/godot,MarianoGnu/godot,sanikoyes/godot,okamstudio/godot,RandomShaper/godot,Max-Might/godot,ex/godot,Marqin/godot,guilhermefelipecgs/godot,Marqin/godot,Marqin/godot,pkowal1982/godot,vnen/godot,zicklag/godot,Faless/godot,NateWardawg/godot,Shockblast/godot,RandomShaper/godot,honix/godot,vnen/godot,ZuBsPaCe/godot,FateAce/godot,groud/godot,guilhermefelipecgs/godot,NateWardawg/godot,ageazrael/godot,Shockblast/godot,MrMaidx/godot,DmitriySalnikov/godot,firefly2442/godot,vkbsb/godot,exabon/godot,Paulloz/godot,MrMaidx/godot,firefly2442/godot,NateWardawg/godot,Max-Might/godot,groud/godot,godotengine/godot,NateWardawg/godot,honix/godot,Zylann/godot,zicklag/godot,MarianoGnu/godot,sanikoyes/godot,DmitriySalnikov/godot,ficoos/godot,akien-mga/godot,Zylann/godot,RandomShaper/godot,DmitriySalnikov/godot,morrow1nd/godot,ZuBsPaCe/godot,Paulloz/godot,Marqin/godot,josempans/godot,MarianoGnu/godot,MrMaidx/godot,NateWardawg/godot,zicklag/godot,firefly2442/godot,NateWardawg/godot,vnen/godot,groud/godot,Valentactive/godot,sanikoyes/godot,morrow1nd/godot,Paulloz/godot,guilhermefelipecgs/godot,ficoos/godot,Shockblast/godot,vkbsb/godot,mcanders/godot,exabon/godot,ageazrael/godot,MrMaidx/godot,okamstudio/godot,jejung/godot,Faless/godot,MarianoGnu/godot,NateWardawg/godot,RebelliousX/Go_Dot,n-pigeon/godot,morrow1nd/godot,okamstudio/godot,exabon/godot,jejung/godot,firefly2442/godot,akien-mga/godot,RebelliousX/Go_Dot,Zylann/godot,pkowal1982/godot,okamstudio/godot,zicklag/godot,RandomShaper/godot,okamstudio/godot,Zylann/godot,BastiaanOlij/godot,BastiaanOlij/godot,firefly2442/godot,godotengine/godot,mcanders/godot,sanikoyes/godot,Paulloz/godot,akien-mga/godot,Brickcaster/godot,n-pigeon/godot,FateAce/godot,DmitriySalnikov/godot,n-pigeon/godot,Shockblast/godot,Faless/godot,sanikoyes/godot,MrMaidx/godot,Valentactive/godot,sanikoyes/godot,exabon/godot,honix/godot,okamstudio/godot,BastiaanOlij/godot,jejung/godot,zicklag/godot,BastiaanOlij/godot,josempans/godot,Valentactive/godot,MarianoGnu/godot,RandomShaper/godot,tomreyn/godot,guilhermefelipecgs/godot,akien-mga/godot,zicklag/godot,Zylann/godot,BastiaanOlij/godot,josempans/godot,Zylann/godot,morrow1nd/godot,FateAce/godot,DmitriySalnikov/godot,godotengine/godot,Shockblast/godot,groud/godot,tomreyn/godot,RandomShaper/godot,ex/godot,akien-mga/godot,Shockblast/godot,ex/godot,morrow1nd/godot,godotengine/godot,MarianoGnu/godot,RebelliousX/Go_Dot,vkbsb/godot,Marqin/godot,vnen/godot,guilhermefelipecgs/godot,honix/godot,MarianoGnu/godot,RebelliousX/Go_Dot,akien-mga/godot,okamstudio/godot,ficoos/godot,josempans/godot,pkowal1982/godot,josempans/godot,ex/godot,vnen/godot,NateWardawg/godot,akien-mga/godot,tomreyn/godot,RebelliousX/Go_Dot,guilhermefelipecgs/godot,honix/godot,BastiaanOlij/godot,groud/godot,Valentactive/godot,ex/godot,exabon/godot,FateAce/godot,Max-Might/godot,Faless/godot,ageazrael/godot,Brickcaster/godot,ageazrael/godot,firefly2442/godot,Brickcaster/godot,Max-Might/godot,vnen/godot,ZuBsPaCe/godot,ageazrael/godot,n-pigeon/godot,vnen/godot,sanikoyes/godot,mcanders/godot,ZuBsPaCe/godot,Valentactive/godot,Faless/godot,honix/godot,ex/godot,guilhermefelipecgs/godot,okamstudio/godot,Valentactive/godot,pkowal1982/godot,NateWardawg/godot,jejung/godot,sanikoyes/godot,pkowal1982/godot,ficoos/godot,mcanders/godot,ex/godot,okamstudio/godot,ZuBsPaCe/godot,josempans/godot,Faless/godot,Shockblast/godot,Paulloz/godot,akien-mga/godot,RebelliousX/Go_Dot,pkowal1982/godot,mcanders/godot,MrMaidx/godot,firefly2442/godot,godotengine/godot,FateAce/godot,godotengine/godot,ficoos/godot,tomreyn/godot,BastiaanOlij/godot,MarianoGnu/godot,n-pigeon/godot,ageazrael/godot,Zylann/godot,jejung/godot,vkbsb/godot,FateAce/godot,Brickcaster/godot,n-pigeon/godot,n-pigeon/godot,vkbsb/godot,Max-Might/godot,morrow1nd/godot,DmitriySalnikov/godot,ZuBsPaCe/godot,vkbsb/godot,vkbsb/godot,RandomShaper/godot,DmitriySalnikov/godot,Marqin/godot,Brickcaster/godot,godotengine/godot,BastiaanOlij/godot,Faless/godot