Use more stable fields for ART class spec offset detection

[AeonLucid]

Hopefully my last PR regarding this. Thanks to @ExternalAddress4401 for providing repro code #361 (comment).

This instance field should not be optimised out, see android code comment https://android.googlesource.com/platform/libcore.git/+/android-4.2.2_r1/luni/src/main/java/java/lang/Thread.java#133.

some of these are accessed directly by the VM; do not rename them

[oleavr]

Thanks! 🙌

[ExternalAddress4401]

Thank you :)

I'll get a test going later and edit my results into this comment.

EDIT: Looks good. Back in business. Thanks again for your hard work getting this fixed.

[as0ler]

Looks like this is failing on Android 16:

{"type":"error","description":"Error: Unable to find copied methods in java/lang/Thread; please file a bug","stack":"Error: Unable to find copied methods in java/lang/Thread; please file a bug\n at /internal-agent.js:1:47232\n at Ie.perform (/internal-agent.js:1:25891)\n at Gn (/internal-agent.js:1:45951)\n at Md (/internal-agent.js:1827:1640)\n at Uo (/internal-agent.js:1827:1258)\n at Function.build (/internal-agent.js:1827:85)\n at t._make (/internal-agent.js:1828:18234)\n at t.use (/internal-agent.js:1828:17033)\n at /internal-agent.js:1837:6963\n at Ie.perform (/internal-agent.js:1:25891)","fileName":"/internal-agent.js","lineNumber":1,"columnNumber":47232}