Re-enable threadLocal option for embedded Java

threadLocal option was disabled in 7.2.52 and upmerged versions, because it was not working correctly (causing cores) if a thread in a threadpool was reused (as is common in Roxie).

Correcting this so that threadLocal can be re-enabled requires a change to the threadTermHook mechanism so that we can distinguish a threadpool end from a thread about to be killed, and a codegen change so that the ICodeContext can be passed per call rather than only at function context creation.