Physics2D: Rename default_density to default_linear_damp
Physics2D: Rename default_density to default_linear_damp

Also adds a proper deprecating warning and tries to do some porting automatically.
Supersedes #4109.

firefly2442/godot,sanikoyes/godot,okamstudio/godot,godotengine/godot,ZuBsPaCe/godot,pkowal1982/godot,ficoos/godot,okamstudio/godot,RandomShaper/godot,okamstudio/godot,opmana/godot,ageazrael/godot,ex/godot,Paulloz/godot,Shockblast/godot,Paulloz/godot,RebelliousX/Go_Dot,zicklag/godot,TheHX/godot,BastiaanOlij/godot,firefly2442/godot,MarianoGnu/godot,mcanders/godot,exabon/godot,Faless/godot,azurvii/godot,guilhermefelipecgs/godot,n-pigeon/godot,Shockblast/godot,Hodes/godot,ZuBsPaCe/godot,jejung/godot,sanikoyes/godot,Zylann/godot,pkowal1982/godot,NateWardawg/godot,vkbsb/godot,godotengine/godot,ex/godot,vnen/godot,MarianoGnu/godot,RandomShaper/godot,JoshuaGrams/godot,Brickcaster/godot,JoshuaGrams/godot,pixelpicosean/my-godot-2.1,NateWardawg/godot,zicklag/godot,okamstudio/godot,josempans/godot,gau-veldt/godot,BastiaanOlij/godot,mcanders/godot,jejung/godot,NateWardawg/godot,guilhermefelipecgs/godot,Hodes/godot,Faless/godot,Marqin/godot,DmitriySalnikov/godot,pixelpicosean/my-godot-2.1,Zylann/godot,BastiaanOlij/godot,honix/godot,Shockblast/godot,NateWardawg/godot,NateWardawg/godot,est31/godot,MarianoGnu/godot,gau-veldt/godot,RebelliousX/Go_Dot,vnen/godot,pkowal1982/godot,Marqin/godot,Valentactive/godot,opmana/godot,n-pigeon/godot,tomreyn/godot,honix/godot,RandomShaper/godot,sanikoyes/godot,vnen/godot,est31/godot,vkbsb/godot,okamstudio/godot,exabon/godot,TheHX/godot,exabon/godot,tomreyn/godot,okamstudio/godot,Brickcaster/godot,Zylann/godot,akien-mga/godot,est31/godot,est31/godot,exabon/godot,Brickcaster/godot,firefly2442/godot,ex/godot,ZuBsPaCe/godot,TheHX/godot,Zylann/godot,rollenrolm/godot,morrow1nd/godot,JoshuaGrams/godot,josempans/godot,Max-Might/godot,ZuBsPaCe/godot,ex/godot,Zylann/godot,sanikoyes/godot,MarianoGnu/godot,vnen/godot,godotengine/godot,ZuBsPaCe/godot,zicklag/godot,ficoos/godot,azurvii/godot,morrow1nd/godot,sanikoyes/godot,josempans/godot,Max-Might/godot,godotengine/godot,rollenrolm/godot,n-pigeon/godot,akien-mga/godot,groud/godot,huziyizero/godot,FateAce/godot,Faless/godot,Marqin/godot,ex/godot,ageazrael/godot,Paulloz/godot,mcanders/godot,josempans/godot,vkbsb/godot,MarianoGnu/godot,n-pigeon/godot,pkowal1982/godot,pixelpicosean/my-godot-2.1,vnen/godot,ageazrael/godot,RandomShaper/godot,MrMaidx/godot,Hodes/godot,azurvii/godot,firefly2442/godot,morrow1nd/godot,akien-mga/godot,honix/godot,jejung/godot,gau-veldt/godot,Faless/godot,JoshuaGrams/godot,Hodes/godot,tomreyn/godot,okamstudio/godot,sanikoyes/godot,tomreyn/godot,groud/godot,exabon/godot,rollenrolm/godot,tomreyn/godot,akien-mga/godot,RebelliousX/Go_Dot,TheHX/godot,vnen/godot,firefly2442/godot,guilhermefelipecgs/godot,jejung/godot,godotengine/godot,RandomShaper/godot,Valentactive/godot,Paulloz/godot,DmitriySalnikov/godot,honix/godot,pixelpicosean/my-godot-2.1,godotengine/godot,jejung/godot,pkowal1982/godot,huziyizero/godot,vkbsb/godot,Valentactive/godot,josempans/godot,RebelliousX/Go_Dot,morrow1nd/godot,guilhermefelipecgs/godot,okamstudio/godot,ex/godot,Max-Might/godot,FateAce/godot,Brickcaster/godot,gau-veldt/godot,Faless/godot,BastiaanOlij/godot,RandomShaper/godot,BastiaanOlij/godot,azurvii/godot,ZuBsPaCe/godot,RebelliousX/Go_Dot,firefly2442/godot,ficoos/godot,akien-mga/godot,vkbsb/godot,honix/godot,okamstudio/godot,Shockblast/godot,akien-mga/godot,DmitriySalnikov/godot,Marqin/godot,morrow1nd/godot,ZuBsPaCe/godot,ficoos/godot,guilhermefelipecgs/godot,ageazrael/godot,pkowal1982/godot,opmana/godot,NateWardawg/godot,okamstudio/godot,Zylann/godot,ex/godot,sanikoyes/godot,josempans/godot,JoshuaGrams/godot,honix/godot,Faless/godot,rollenrolm/godot,Valentactive/godot,opmana/godot,Paulloz/godot,Max-Might/godot,Paulloz/godot,firefly2442/godot,huziyizero/godot,josempans/godot,exabon/godot,huziyizero/godot,Paulloz/godot,zicklag/godot,FateAce/godot,BastiaanOlij/godot,est31/godot,n-pigeon/godot,guilhermefelipecgs/godot,azurvii/godot,MrMaidx/godot,Zylann/godot,NateWardawg/godot,n-pigeon/godot,DmitriySalnikov/godot,azurvii/godot,Valentactive/godot,Hodes/godot,Zylann/godot,huziyizero/godot,Max-Might/godot,Valentactive/godot,MarianoGnu/godot,groud/godot,opmana/godot,mcanders/godot,DmitriySalnikov/godot,FateAce/godot,Marqin/godot,ex/godot,godotengine/godot,zicklag/godot,NateWardawg/godot,guilhermefelipecgs/godot,FateAce/godot,gau-veldt/godot,MrMaidx/godot,ageazrael/godot,Valentactive/godot,groud/godot,guilhermefelipecgs/godot,Faless/godot,vnen/godot,ageazrael/godot,Max-Might/godot,Marqin/godot,Hodes/godot,Shockblast/godot,ficoos/godot,BastiaanOlij/godot,Brickcaster/godot,MrMaidx/godot,MarianoGnu/godot,JoshuaGrams/godot,ficoos/godot,Faless/godot,firefly2442/godot,akien-mga/godot,godotengine/godot,vnen/godot,groud/godot,sanikoyes/godot,RandomShaper/godot,pkowal1982/godot,MrMaidx/godot,pkowal1982/godot,ageazrael/godot,Brickcaster/godot,MrMaidx/godot,DmitriySalnikov/godot,ZuBsPaCe/godot,vkbsb/godot,TheHX/godot,jejung/godot,zicklag/godot,mcanders/godot,Brickcaster/godot,NateWardawg/godot,RebelliousX/Go_Dot,FateAce/godot,mcanders/godot,est31/godot,akien-mga/godot,rollenrolm/godot,Shockblast/godot,groud/godot,BastiaanOlij/godot,n-pigeon/godot,josempans/godot,pixelpicosean/my-godot-2.1,vkbsb/godot,Shockblast/godot,MarianoGnu/godot,morrow1nd/godot,vkbsb/godot,Shockblast/godot,DmitriySalnikov/godot,Valentactive/godot