Rename `ProgressToken.Chunk` to `Slice` #538

Job	Run time
csproj-build (Release, true)	51s
csproj-build (Release, false)	50s
csproj-build (Release_NoProgress, true)	49s
csproj-build (Release_NoProgress, false)	49s
csproj-build (Debug, true)	47s
csproj-build (Debug, false)	46s
csproj-build (Debug_NoProgress, true)	45s
csproj-build (Debug_NoProgress, false)	48s
	6m 25s

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