RepositoryCache: add blake3 key type

Support storing repository cache with blake3 hash function.

Closes #21998.

PiperOrigin-RevId: 625727463
Change-Id: I2198adac617c5d6301e56694fe416f3130c61033
diff --git a/src/test/java/com/google/devtools/build/lib/testutil/TestConstants.java b/src/test/java/com/google/devtools/build/lib/testutil/TestConstants.java
index 09ee8d6..43ae402 100644
--- a/src/test/java/com/google/devtools/build/lib/testutil/TestConstants.java
+++ b/src/test/java/com/google/devtools/build/lib/testutil/TestConstants.java
@@ -187,6 +187,9 @@
   /** The cpp toolchain type. */
   public static final String CPP_TOOLCHAIN_TYPE = "@@bazel_tools//tools/cpp:toolchain_type";
 
+  /** Whether blake3 can be used through JNI */
+  public static final boolean BLAKE3_AVAILABLE = true;
+
   /** A choice of test execution mode, only varies internally. */
   public enum InternalTestExecutionMode {
     NORMAL