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

Job	Run time
Syntax Check - Clang C++03 Linux No STL (ubuntu-22.04)	26s
Syntax Check - Clang C++03 Linux STL (ubuntu-22.04)	23s
Syntax Check - Clang C++11 Linux No STL (ubuntu-22.04)	38s
Syntax Check - Clang C++11 Linux No STL Force C++03 (ubuntu-22.04)	38s
Syntax Check - Clang C++11 Linux STL (ubuntu-22.04)	37s
Syntax Check - Clang C++11 Linux STL Force C++03 (ubuntu-22.04)	37s
Syntax Check - Clang C++14 Linux No STL Force C++03 (ubuntu-22.04)	41s
Syntax Check - Clang C++14 Linux No STL (ubuntu-22.04)	36s
Syntax Check - Clang C++14 Linux STL (ubuntu-22.04)	42s
Syntax Check - Clang C++14 Linux STL Force C++03 (ubuntu-22.04)	42s
Syntax Check - Clang C++17 Linux No STL (ubuntu-22.04)	50s
Syntax Check - Clang C++17 Linux STL (ubuntu-22.04)	1m 1s
Syntax Check - Clang C++17 Linux No STL Force C++03 (ubuntu-22.04)	42s
Syntax Check - Clang C++17 Linux STL Force C++03 (ubuntu-22.04)	53s
Syntax Check - Clang C++20 Linux No STL (ubuntu-22.04)	59s
Syntax Check - Clang C++20 Linux No STL Force C++03 (ubuntu-22.04)	1m 3s
Syntax Check - Clang C++20 Linux STL (ubuntu-22.04)	1m 23s
Syntax Check - Clang C++20 Linux STL Force C++03 (ubuntu-22.04)	1m 15s
	14m 6s

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