fsxc: always deliver a LineKind for each line #1909

Job	Run time
linux-newLTS-vanilla--dotnet6	6m 47s
linux-newLTS-github--dotnet-and-xbuild	6m 24s
linux-newLTS-github--dotnet-and-msbuild	6m 45s
linux-newLTS-vanilla--newmono	5m 15s
linux-newLTS-vanilla--stockmono	4m 11s
linux-oldLTS-github--dotnet-and-msbuild	6m 40s
linux-oldLTS-vanilla--newmono	5m 28s
linux-oldLTS-github--dotnet-and-xbuild	6m 10s
linux-oldLTS-vanilla--stockmono	4m 46s
macOS--dotnet6-and-mono	6m 28s
macOS--mono	4m 58s
windows--dotnet6	7m 55s
windows--legacyFramework	13m 18s
sanity-check	1m 3s
publish	0s
	1h 26m 8s

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