Add contains() method to etl::unordered_map and etl::unordered_set #526

Job	Run time
Syntax Check - GCC C++03 Linux STL (ubuntu-22.04)	17s
Syntax Check - GCC C++11 Linux STL (ubuntu-22.04)	28s
Syntax Check - GCC C++03 Linux No STL (ubuntu-22.04)	17s
Syntax Check - GCC C++11 Linux No STL (ubuntu-22.04)	23s
Syntax Check - GCC C++11 Linux No STL Force C++03 (ubuntu-22.04)	24s
Syntax Check - GCC C++11 Linux STL Force C++03 (ubuntu-22.04)	24s
Syntax Check - GCC C++14 Linux No STL (ubuntu-22.04)	24s
Syntax Check - GCC C++14 Linux No STL Force C++03 (ubuntu-22.04)	27s
Syntax Check - GCC C++14 Linux STL (ubuntu-22.04)	27s
Syntax Check - GCC C++14 Linux STL Force C++03 (ubuntu-22.04)	27s
Syntax Check - GCC C++17 Linux No STL (ubuntu-22.04)	29s
Syntax Check - GCC C++17 Linux No STL Force C++03 (ubuntu-22.04)	30s
Syntax Check - GCC C++17 Linux STL (ubuntu-22.04)	36s
Syntax Check - GCC C++17 Linux STL Force C++03 (ubuntu-22.04)	36s
Syntax Check - GCC C++20 Linux No STL (ubuntu-22.04)	45s
Syntax Check - GCC C++20 Linux No STL Force C++03 (ubuntu-22.04)	42s
Syntax Check - GCC C++20 Linux STL (ubuntu-22.04)	52s
Syntax Check - GCC C++20 Linux STL Force C++03 (ubuntu-22.04)	50s
	9m 18s

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