add effective user context manipulation routines #5203

Job	Run time
macos/clang++/c++17	3m 54s
macos/clang++/c++17	3m 54s
macos/clang++/c++17	3m 54s
macos/clang++/c++17	3m 54s
macos/clang++/c++17	3m 54s
buster/g++/c++17/asan=off/ubsan=off	7m 15s
buster/g++/c++17/asan=off/ubsan=off	7m 15s
buster/g++/c++17/asan=off/ubsan=off	7m 15s
buster/g++/c++17/asan=off/ubsan=off	1s
buster/g++/c++17/asan=off/ubsan=off	1s
focal/clang++/c++17/asan=off/ubsan=on	7m 15s
focal/clang++/c++17/asan=off/ubsan=on	19m 1s
focal/clang++/c++17/asan=off/ubsan=on	19m 1s
focal/clang++/c++17/asan=off/ubsan=on	19m 1s
focal/clang++/c++17/asan=off/ubsan=on	19m 1s
focal/g++-10/c++20/asan=on/ubsan=off	7m 13s
focal/g++-10/c++20/asan=on/ubsan=off	7m 13s
focal/g++-10/c++20/asan=on/ubsan=off	7m 38s
focal/g++-10/c++20/asan=on/ubsan=off	7m 38s
focal/g++-10/c++20/asan=on/ubsan=off	7m 38s
jammy/g++/c++20/asan=on/ubsan=off	6m 59s
jammy/g++/c++20/asan=on/ubsan=off	6m 59s
jammy/g++/c++20/asan=on/ubsan=off	6m 59s
jammy/g++/c++20/asan=on/ubsan=off	6m 59s
jammy/g++/c++20/asan=on/ubsan=off	6m 59s
	3h 16m 51s

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