RFR (S): 8191904: Refactor weak oops in ResolvedMethodTable to use the Access API

[Erik Österlund]

Hi,

The ResolvedMethodTable has weak oop references in it. Currently it uses 
explicit SATB enqueueing for G1 to make the weak semantics work.

This should be refactored to use the Access API instead. The previous 
raw loads should be ON_PHANTOM_OOP | AS_NO_KEEPALIVE and the loads 
followed by explicit G1 SATB enqueueing should be ON_PHANTOM_OOP.

Webrev:
http://cr.openjdk.java.net/~eosterlund/8191904/webrev.00/

Bug:
https://bugs.openjdk.java.net/browse/JDK-8191904

Thanks,
/Erik