fix: use android.jar as bootstrapClasspath

[shifujun]

Some projects like aosp-dexutils are using java-library plugin,
but they are used in Android platform.
That means it compiled against standard JDK, maybe JDK11,
but run under android.jar.

We should set android.jar as bootstrapClasspath of javac,
like com.android.library did.

Before this commit:

#verify use JDK11
javac --version
javac 11.0.11

#compile a java-library project
./gradlew :third-party:aosp-dexutils:compileJava
BUILD SUCCESSFUL

# disassemble class and check target method signature
javap -c -verbose third-party/aosp-dexutils/build\
/classes/java/main/com/tencent/tinker/android/dex/Dex.class \
| grep 'Method java/nio/ByteBuffer.position'

# output contains:
java/nio/ByteBuffer.position:(I)Ljava/nio/ByteBuffer;

After this commit, output change to:

java/nio/ByteBuffer.position:(I)Ljava/nio/Buffer;