Make macos version work (testes on m1 at least)

1. Change name of discord's library to libdiscord_game_sdk, so it
links properly
2. Change it's install name with install_name_tool to use @loader_path
instead of @rpath, that one's a blunder on discord's side, it should
really have been loader_path from the beginning (rpath means look at
where the binary is started from, loader_path means look at where the
library is)
3. Combine the aarch and x86 library into one, again no idea why
discord does not do this themselves

SConstruct

@@ -4,8 +4,8 @@ import os
 env = SConscript("src/lib/godot-cpp/SConstruct")
 
 if env["platform"] == "macos":
-    discord_library = "discord_game_sdk.dylib"
-    discord_library_second = "discord_game_sdk_aarch64.dylib"
+    discord_library = "libdiscord_game_sdk.dylib"
+    discord_library_second = ""
     libexportfolder = "/macos/"
 
 elif env["platform"] in ("linuxbsd", "linux"):