add feature dwarf #385

Job	Run time
Dwarf feature	48m 44s
Conformance Tests	31m 39s
build (macos-11, stable)	7m 2s
build (macos-11, 1.48.0)	12m 11s
Cargo fmt	8s
build (windows-2019, stable)	8m 4s
build (windows-2019, 1.48.0)	14m 42s
build (ubuntu-20.04, stable)	9m 27s
build (ubuntu-20.04, 1.48.0)	13m 21s
build (ubuntu-20.04, nightly)	11m 10s
build (ubuntu-20.04, beta)	10m 25s
build (ubuntu-20.04, i686-unknown-linux-gnu, stable)	8m 15s
build (windows-2019, i686-pc-windows-msvc, stable)	7m 32s
build (ubuntu-20.04, clang, clang++, stable)	5m 45s
build (ubuntu-20.04, gcc-7, g++-7, stable)	6m 40s
build (ubuntu-20.04, clang-7, clang++-7, stable)	5m 24s
	3h 20m 29s

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