Add RTLIL "buffered-normalized mode" and improve "bufnorm" pass #2245

Job	Run time
test-linux (ubuntu-20.04, focal, clang-12, c++11)	15m 36s
test-linux (ubuntu-20.04, focal, clang-12, c++14)	14m 59s
test-linux (ubuntu-20.04, focal, clang-12, c++17)	14m 26s
test-linux (ubuntu-20.04, focal, clang-12, c++20)	14m 28s
test-linux (ubuntu-20.04, focal, gcc-11, c++11)	33m 47s
test-linux (ubuntu-20.04, focal, gcc-11, c++14)	18m 14s
test-linux (ubuntu-20.04, focal, gcc-11, c++17)	15m 16s
test-linux (ubuntu-20.04, focal, gcc-11, c++20)	15m 10s
test-linux (ubuntu-20.04, focal, clang-11, c++11)	14m 28s
test-linux (ubuntu-20.04, focal, gcc-10, c++11)	15m 59s
	2h 52m 23s

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