Make JUnit 5 the default test framework

Summary:
JUnit 4 has been in maintenance mode and the Java Foundation team has been
migrating tests to JUnit 5 since January 2026. This diff completes the
infrastructure side of the migration by making JUnit 5 the default for
java_test targets.

Changes:
- java_test() macro now defaults to test_type = "junit5" (kotlin_test is unchanged)
- Auto-inject JUnit 5 dependencies (jupiter-api, jupiter-engine, platform-launcher) for junit5 targets, mirroring how JUnit 4 deps were previously auto-injected
- All 194 existing java_test targets that relied on the implicit JUnit 4 default now have explicit test_type = "junit" to preserve their behavior

Going forward:
- New java_test targets use JUnit 5 by default
- To use JUnit 4, set test_type = "junit" explicitly
- The existing JUnit 5 migration codemod (CodemodConfigDevmateJavaJunitMigrator) will continue converting test_type = "junit" targets to "junit5" with source-level import changes

Reviewed By: j-bahr

Differential Revision: D95378663

fbshipit-source-id: ef5287815f6f7520a4210b8a49ec9b234cdab127

Author: RayanRal

watchman/java/BUCK

@@ -54,6 +54,7 @@ java_test(
     srcs = glob(["test/**/*.java"]),
     source = "7",
     target = "7",
+    test_type = "junit",
     deps = [
         ":watchman-lib",
         "//third-party/guava:guava",