Fix name of method symbols (__extensions__)

[brson]

Examples of method names.

+ 1.97% coroutine-call coroutine-call [.] rt::comm::__extensions__::try_recv_4749::anon::expr_fn_4752 ▒
+ 1.94% coroutine-call libcore-c3ca5d77d81b46c1-0.7-pre.so [.] rt::sched::__extensions__::meth_24322::resume_task_from_queue::_98d7edf54cd03ca::_07pre ▒
+ 1.92% coroutine-call librustrt.so [.] upcall_call_shim_on_rust_stack ▒
+ 1.76% coroutine-call libcore-c3ca5d77d81b46c1-0.7-pre.so [.] rt::uv::idle::__extensions__::idle_cb::_102cdea612f47982::_07pre ▒
+ 1.74% coroutine-call libcore-c3ca5d77d81b46c1-0.7-pre.so [.] rt::sched::__extensions__::meth_24416::enqueue_cleanup_job::_5bddff916a99173::_07pre ▒
+ 1.72% coroutine-call libcore-c3ca5d77d81b46c1-0.7-pre.so [.] _ZN2rt5sched11local_sched19rust_get_rt_tls_key16_585f1373eca8c836_07preE@plt ▒
+ 1.72% coroutine-call [vdso] [.] 0x00007fff543ff894 ▒
+ 1.53% coroutine-call coroutine-call [.] rt::comm::__extensions__::try_recv_4641::_2880c2c982aa795::_00 ▒
+ 1.34% coroutine-call libcore-c3ca5d77d81b46c1-0.7-pre.so [.] rt::uv::idle::__extensions__::close_cb::__rust_stack_shim ▒
+ 1.34% coroutine-call libcore-c3ca5d77d81b46c1-0.7-pre.so [.] rt::sched::__extensions__::meth_20718::resume_task_immediately::_cb9890c6b348544::_07pre ▒
+ 1.32% coroutine-call libcore-c3ca5d77d81b46c1-0.7-pre.so [.] rt::sched::__extensions__::meth_16410::schedule_task::_cb9890c6b348544::_07pre ▒
+ 1.31% coroutine-call libcore-c3ca5d77d81b46c1-0.7-pre.so [.] rt::sched::__extensions__::schedule_task::anon::expr_fn_24410 ▒
+ 1.30% coroutine-call libcore-c3ca5d77d81b46c1-0.7-pre.so [.] rt::uv::idle::__extensions__::idle_cb::__rust_stack_shim ▒
+ 1.29% coroutine-call coroutine-call [.] rt::comm::__extensions__::try_recv_4641::anon::expr_fn_4644 ▒
+ 1.25% coroutine-call libcore-c3ca5d77d81b46c1-0.7-pre.so [.] rt::uv::uvio::__extensions__::callback::anon::expr_fn_25096 ▒
+ 1.11% coroutine-call libcore-c3ca5d77d81b46c1-0.7-pre.so [.] rt::uv::uvio::__extensions__::meth_24318::callback::_cad8f2676061ef2a::_07pre 

Use a meaningful symbol name instead of __extensions__::meth_INTEGER.

[brson]

Nominating.

[graydon]

nominating for what milestone?

[graydon]

is this an artifact of when we had named impls?

[graydon]

accepted for production-ready milestone

[bblum]

I think this is such an artifact as graydon asks. I don't know if it's strictly necessary.