deps: update fmt to latest version (#3403)

This updates `fmt` to the latest version and moves to just being a copy
of their repo to make updating easier (no editing their cmake / figuring
out which files to minimally include).

The motivation for this is now that we switched to C++ 20, there were a
ton of deprecated function usages that is going away in future compiler
versions. This gets rid of all those warnings.

decompiler/data/StrFileReader.cpp

@@ -13,7 +13,7 @@
 #include "game/common/overlord_common.h"
 #include "game/common/str_rpc_types.h"
 
-#include "third-party/fmt/format.h"
+#include "fmt/format.h"
 
 namespace decompiler {
 StrFileReader::StrFileReader(const fs::path& file_path, GameVersion version) : m_version(version) {