Use one option for controlling debug symbols

[dustdfg]

It seems a bit strange to me that we have two separate options debug_symbols and separate_debug_symbols both with yes/no values. I guess it was added for compatibility but.... Why not to have one option? debug_symbols with possible values: none/separate/(embedded|builtin).

Does it have much sense? No, but it is strange.

[Calinou]

Thanks for the proposal! Consolidating in godotengine/godot#72247.