More BUILD file refactorings.

Split collect, concurrent, vfs, windows into package-level BUILD files.
Move clock classes out of "util", into their own Java package.
Move CompactHashSet into its own Java package to break a dependency cycle.
Give nestedset and inmemoryfs their own package-level BUILD files.

PiperOrigin-RevId: 167702127
diff --git a/src/main/java/com/google/devtools/build/lib/runtime/BuildSummaryStatsModule.java b/src/main/java/com/google/devtools/build/lib/runtime/BuildSummaryStatsModule.java
index 0805acd..f61d833 100644
--- a/src/main/java/com/google/devtools/build/lib/runtime/BuildSummaryStatsModule.java
+++ b/src/main/java/com/google/devtools/build/lib/runtime/BuildSummaryStatsModule.java
@@ -19,13 +19,13 @@
 import com.google.devtools.build.lib.buildtool.BuildRequest;
 import com.google.devtools.build.lib.buildtool.buildevent.BuildCompleteEvent;
 import com.google.devtools.build.lib.buildtool.buildevent.ExecutionStartingEvent;
+import com.google.devtools.build.lib.clock.BlazeClock;
 import com.google.devtools.build.lib.events.Event;
 import com.google.devtools.build.lib.events.Reporter;
 import com.google.devtools.build.lib.exec.ExecutionOptions;
 import com.google.devtools.build.lib.exec.ExecutorBuilder;
 import com.google.devtools.build.lib.profiler.Profiler;
 import com.google.devtools.build.lib.profiler.ProfilerTask;
-import com.google.devtools.build.lib.util.BlazeClock;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.logging.Logger;