RFR (M) 8203837: Split nmethod unloading from nmethod cache cleaning

[coleen.phillimore at oracle.com]

Summary: Refactor cleaning inline caches to after GC do_unloading.

See CR for more information.  This patch refactors 
CompiledMethod::do_unloading() to unload nmethods in case of !is_alive 
oop.  If the nmethod is not unloaded, cleans the inline caches, and 
exception cache, for unloaded classes and unloaded nmethods.  The 
CodeCache walk in gc_epilogue is moved earlier to combine with cleanup 
for class unloading.

It doesn't add CodeCache walks to any of the GCs, and keeps the G1 
parallel nmethod unloading intact.  This patch also uses common code for 
CompiledMethod::clean_inline_caches which was duplicated by the G1 
functions.

The patch also fixed a case in AOT where clear_inline_caches should be 
called instead of clean_inline_caches.   I think neither is necessary 
for the nmethods that are deoptimized because of redefinition, but 
clear_inline_caches clears up redefined Methods* not for unloaded 
nmethods.  Once the method is cleaned by the sweeper, 
clean_inline_caches will be called on it.  clear vs. clean ...

The patch also converts TraceScavenge to -Xlog:gc+nmethod=trace.  I can 
revert this part and do it separately; I had just converted it while 
looking at the output.

open webrev at http://cr.openjdk.java.net/~coleenp/8203837.01/webrev
bug link https://bugs.openjdk.java.net/browse/JDK-8203837

Tested with mach5 hs-tier1-5, the gc-test-suite (including specjbb2015, 
dacapo, gcbasher), runThese with all GCs with and without class unloading.

This is an enhancement that we can use for making nmethod cleaning 
concurrent in ZGC.

Thanks,
Coleen