Add hud-set-xstr sexp #4738

Job	Run time
Windows (Debug, MSVC, Win32)	15m 31s
Windows (Debug, MSVC, x64)	13m 23s
Mac (Debug, clang, x86_64)	7m 6s
Windows (Release, MSVC, Win32)	19m 30s
Mac (Debug, clang, arm64)	6m 3s
Linux (Debug, gcc-9)	11m 59s
Mac (Release, clang, x86_64)	6m 7s
Windows (Release, MSVC, x64)	19m 29s
Linux (Debug, gcc-13)	10m 27s
Mac (Release, clang, arm64)	5m 52s
Linux (Debug, clang-16)	11m 40s
Linux (Release, gcc-9)	8m 21s
Linux (Release, gcc-13)	9m 10s
Linux (Release, clang-16)	11m 11s
Linux (Debug, gcc-13, -DFSO_BUILD_WITH_OPENGL=OFF -DFSO_BUILD_WITH_VULKAN=OFF)	9m 26s
Linux (Release, gcc-13, -DFSO_BUILD_WITH_OPENGL=OFF -DFSO_BUILD_WITH_VULKAN=OFF)	9m 28s
	2h 54m 43s

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