TEST_CASE_FIXTURE: A new fixture macro for allowing persistent fixtures throughout a TEST_CASE #1804

Job	Run time
Surrogates build, clang++-10, C++14 Debug	1m 15s
clang-tidy 15, all, C++17 Debug	5m 43s
Extras + Examples, g++-7, C++14 Debug	2m 59s
Extras + Examples, g++-7, C++14 Release	3m 6s
Extras + Examples, clang++-10, C++17 Debug	3m 11s
Extras + Examples, clang++-10, C++17 Release	3m 56s
CMake configuration tests, clang++-10, C++14 Debug	3m 6s
Valgrind tests, clang++-10, C++14 Debug	3m 9s
	26m 25s

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