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.

common/util/FontUtils.cpp

@@ -16,8 +16,8 @@
 
 #include "common/util/Assert.h"
 
-#include "third-party/fmt/core.h"
-#include "third-party/fmt/format.h"
+#include "fmt/core.h"
+#include "fmt/format.h"
 
 const std::unordered_map<std::string, GameTextVersion> sTextVerEnumMap = {
     {"jak1-v1", GameTextVersion::JAK1_V1},