write: add `LineConvert` #528

Job	Run time
coverage	1m 4s
Build fuzz targets	1m 6s
build (ubuntu-latest, stable)	47s
bench	1m 3s
cross (i686-unknown-linux-gnu)	41s
build (ubuntu-latest, beta)	44s
cross (powerpc64-unknown-linux-gnu)	46s
doc	20s
build (ubuntu-latest, nightly)	42s
features	3m 3s
build (stable, macOS-latest)	41s
msrv	2m 35s
msrv-read	2m 36s
rustfmt	5s
Run `debug_abbrev` fuzz target	5m 9s
Run `debug_aranges` fuzz target	5m 6s
Run `debug_info` fuzz target	5m 6s
Run `debug_line` fuzz target	5m 6s
Run `eh_frame` fuzz target	5m 5s
Run `eh_frame_hdr` fuzz target	5m 6s
	46m 51s

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