BufferLine rewrite [WIP] #568

Job	Run time
build	1m 0s
lint	56s
test-api-parallel (18, ubuntu, chromium)	2m 27s
test-playwright-parallel (18, ubuntu, chromium)	1m 56s
test-unit-parallel (18, ubuntu)	1m 27s
test-api-parallel (18, ubuntu, firefox)	2m 48s
test-playwright-parallel (18, ubuntu, firefox)	1m 51s
test-unit-parallel (18, macos)	1m 34s
test-playwright-parallel (18, ubuntu, webkit)	1m 47s
test-unit-parallel (18, windows)	1m 28s
test-unit-coverage	58s
release-dry-run (18)	1m 47s
test-api (18, windows, chromium)	6m 17s
test-api (18, windows, firefox)	6m 11s
	32m 27s

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