Add new targets to run rustfmt for Rust projects #17112

Job	Run time
Arch Linux	20m 0s
CUDA (on Arch)	7m 54s
Arch / PyPy	20m 54s
Fedora	17m 40s
Gentoo	22m 13s
Ubuntu Rolling (gcc, g++)	18m 52s
OpenSUSE	17m 20s
Ubuntu Rolling (--unity=on -Ddefault_library=static, --no-unittests, gcc, g++)	13m 35s
Ubuntu Bionic	16m 11s
Ubuntu Rolling (-Ddefault_library=both, --no-unittests, gcc, g++)	13m 45s
Ubuntu Rolling (clang, clang++)	21m 28s
Ubuntu Rolling (--unity=on, --no-unittests, clang, clang++)	14m 47s
Ubuntu Rolling (--cross ubuntu-armhf.json --cross linux-mingw-w64-64bit.json, 0, gcc, g++)	13m 35s
Ubuntu Rolling (--cross ubuntu-armhf.json --cross linux-mingw-w64-64bit.json, --unity=on, gcc, g++)	14m 32s
	3h 52m 46s

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