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/test/java/com/google/devtools/build/lib/pkgcache/IncrementalLoadingTest.java b/src/test/java/com/google/devtools/build/lib/pkgcache/IncrementalLoadingTest.java
index 829e1c8..9eb5b20 100644
--- a/src/test/java/com/google/devtools/build/lib/pkgcache/IncrementalLoadingTest.java
+++ b/src/test/java/com/google/devtools/build/lib/pkgcache/IncrementalLoadingTest.java
@@ -22,6 +22,7 @@
 import com.google.common.collect.ImmutableMap;
 import com.google.common.eventbus.EventBus;
 import com.google.devtools.build.lib.analysis.BlazeDirectories;
+import com.google.devtools.build.lib.clock.BlazeClock;
 import com.google.devtools.build.lib.cmdline.Label;
 import com.google.devtools.build.lib.events.Reporter;
 import com.google.devtools.build.lib.packages.ConstantRuleVisibility;
@@ -42,7 +43,6 @@
 import com.google.devtools.build.lib.syntax.SkylarkSemanticsOptions;
 import com.google.devtools.build.lib.testutil.ManualClock;
 import com.google.devtools.build.lib.testutil.TestConstants;
-import com.google.devtools.build.lib.util.BlazeClock;
 import com.google.devtools.build.lib.util.Preconditions;
 import com.google.devtools.build.lib.util.io.TimestampGranularityMonitor;
 import com.google.devtools.build.lib.vfs.Dirent;