Clarify SNAME usage
Clarify SNAME usage

* Explain where it should be used, with examples.
* Clarify that it should _not_ be used everywhere, only where needed.
* Supersedes #57720

This PR is the result of the discussion that happened in a contractor meeting, and it attempts to clarify the intended use for this macro for other contributors.
As a personal note, It is my view that other approaches to using SNAME (like having a global or per class table of string names) are mere overengineering without any real benefit (performance remains the same, and usage of stringnames becomes more cumbersome. Additionally, there was not any significant amount of errors in name mismatching as a result of using strings since Godot was open sourced).

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