RFR: 8272723: Don't use Access API to access primitive fields [v2]

[Roman Kennke]

> For earlier incarnations of Shenandoah, we needed to put barriers before accessing primitive fields. This is no longer necessary nor implemented/used by any GC, and we should simplify the code to do plain access instead.
> 
> (We may want to remove remaining primitive access machinery in the Access API soon)
> 
> Testing:
>  - [ ] tier1
>  - [ ] tier2
>  - [ ] hotspot_gc

Roman Kennke has updated the pull request incrementally with one additional commit since the last revision:

  Remove remaining primitive Access API uses

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/5187/files
  - new: https://git.openjdk.java.net/jdk/pull/5187/files/beb6b9c8..82366c30

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=5187&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=5187&range=00-01

  Stats: 136 lines in 5 files changed: 4 ins; 62 del; 70 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5187.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5187/head:pull/5187

PR: https://git.openjdk.java.net/jdk/pull/5187