use @FastNative annotation for Android to speed up JNI calls

[kaitian521]

Let's talk about an interesting topic

https://developer.android.com/reference/dalvik/annotation/optimization/FastNative

========= my test ==========

        MMKV mmkv = MMKV.defaultMMKV();
        mmkv.encode("key", 1L);

        long start = System.currentTimeMillis();
        for (int i = 0; i < 1000000; i++) {
            long v = mmkv.decodeLong("key");
        }
        long duration = System.currentTimeMillis() - start;
        Log.e("lishaokai", "running duration = " + duration);

when adding @fastNative, running duration is 915ms

//    @FastNative
    private native long decodeLong(long handle, String key, long defaultValue);

when delete @fastNative, running duration is 1030ms

almost 10% speed up

so I just am curious about adding this annotation to speed up JNI calls for some special functions such as decodeX()
what's more, AOSP are using it, such as

https://github.com/aosp-mirror/platform_frameworks_base/blob/da436ad3e31f95eae922519ff1cbcf90b60900cb/core/java/android/os/Trace.java#L130

Thank you

[lingol]

Thanks for your input. I didn't know about that annotation until now.