Upgrade fmt dependency to v10.2.1 (#6869)

* Put fmt into version agnostic subdir

* Add fmt to dependency update script

* Remove manually added fmt

* Squashed 'third_party/fmt/' content from commit e69e5f977

git-subtree-dir: third_party/fmt
git-subtree-split: e69e5f977d458f2650bb346dadf2ad30c5320281

third_party/fmt/.gitignore

@@ -0,0 +1,24 @@
+*.a
+*.so*
+*.xcodeproj
+*~
+.vscode/
+/CMakeScripts
+/Testing
+/_CPack_Packages
+/doc/doxyxml
+/doc/html
+/doc/node_modules
+/install_manifest.txt
+CMakeCache.txt
+CMakeFiles
+CPack*.cmake
+CTestTestfile.cmake
+FMT.build
+Makefile
+bin/
+build/
+cmake_install.cmake
+fmt-*.cmake
+fmt.pc
+virtualenv