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/runtime/TestSummaryTest.java b/src/test/java/com/google/devtools/build/lib/runtime/TestSummaryTest.java
index 7ea22b3..0ea18af 100644
--- a/src/test/java/com/google/devtools/build/lib/runtime/TestSummaryTest.java
+++ b/src/test/java/com/google/devtools/build/lib/runtime/TestSummaryTest.java
@@ -25,8 +25,8 @@
 
 import com.google.common.collect.ImmutableList;
 import com.google.devtools.build.lib.analysis.ConfiguredTarget;
+import com.google.devtools.build.lib.clock.BlazeClock;
 import com.google.devtools.build.lib.cmdline.Label;
-import com.google.devtools.build.lib.util.BlazeClock;
 import com.google.devtools.build.lib.util.io.AnsiTerminalPrinter;
 import com.google.devtools.build.lib.vfs.FileSystem;
 import com.google.devtools.build.lib.vfs.FileSystemUtils;