android_sdk: Host JVM test runner for PerfettoTraceTest

Companion to tools/run_android_test (which runs the SDK test under ART on
a device or emulator). tools/run_android_sdk_host_test compiles the
upstream perfetto Java SDK against a small set of host-only stubs for the
android.* classes the SDK references, links against the standard
libperfetto_jni.so the gn+ninja pipeline produces, and runs the JUnit
suite under whatever host JVM is on PATH.

Mechanics
---------
* Stubs at src/android_sdk/java/host_stubs/ cover the only Android
  symbols the SDK + test touch: dalvik.annotation.optimization.{Critical,
  Fast}Native (no-op annotations), android.system.SystemCleaner (delegates
  to java.lang.ref.Cleaner), android.util.{ArraySet,Log},
  android.os.Process, and androidx.test.ext.junit.runners.AndroidJUnit4
  (delegates to BlockJUnit4ClassRunner). Same .java sources compile and
  run on both Android and host -- no codegen, no patched SDK file.
* libperfetto_jni's source set gains a conditional include path
  (jdk_include_path, opt-in via tools/gn args) that wires up the host
  JDK's jni.h and a small android/log.h shim under host_shims/. AOSP /
  device builds are untouched because the conditional only fires when
  jdk_include_path is set, which the runner does itself when the user
  invokes it.
* tools/install-build-deps --java-sdk lands JUnit 4, Hamcrest, Truth,
  Guava + failureaccess, protobuf-java 4.31.1 (matches protoc 31.x),
  error_prone_annotations, checker-qual and j2objc-annotations in
  buildtools/java_sdk_host_test/. All SHA256-pinned from Maven Central.
  The flag is opt-in -- a plain tools/install-build-deps doesn't pull
  Java deps, so the standard build is unaffected.
* The runner generates the Java proto codegen for the transitive
  closure of imports starting from the protos PerfettoTraceTest
  references, javac-compiles SDK + stubs + protos to
  out/release/perfetto_sdk_host.jar, compiles the test to
  perfetto_sdk_host_test.jar, and invokes JUnitCore with java.library.path
  + LD_LIBRARY_PATH pointing at out/release.

Why the macro + this runner together
------------------------------------
Running the upstream SDK natives under HotSpot requires the standard
JNIEnv*/jclass prefix on the C side; PERFETTO_JNI_HOST_PARAMS handles
that. This change adds the surrounding glue (host stubs + native build
wiring + JUnit driver) so contributors can iterate on the Java SDK on
their dev machine without a connected device or emulator. C++ tests and
benchmarks (perfetto_unittests / perfetto_benchmarks) already run on
host; this closes the same loop for the Java side.

Usage
-----
  tools/install-build-deps
  tools/install-build-deps --java-sdk
  tools/run_android_sdk_host_test
  # -> "OK (20 tests)" on HotSpot 21

Verification
------------
PerfettoTraceTest -> 20/20 PASS on host OpenJDK 21 (3.08s).
AOSP / device build path unaffected: jdk_include_path defaults to "" so
the new include_dirs and cflags blocks in libperfetto_jni_src are inert
unless the runner is in use.

Change-Id: If4b9451acc9d3381a597ef9661f245e7bcdb342b