RFR: 8296349: [aarch64] Avoid slicing Address::extend [v2]

[Kim Barrett]

> Please review this change around `Address::extend`.  The 4 derived classes are
> replaced by static functions of the same name as the former class.  These
> functions return an `extend` object initialized with the same values as were
> used by the corresponding derived class constructor.
> 
> Testing: mach5 tier1-3

Kim Barrett has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains two additional commits since the last revision:

 - Merge branch 'master' into flatten-extend
 - flatten Address::extend

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/10976/files
  - new: https://git.openjdk.org/jdk/pull/10976/files/a351cd6a..77ac8cdd

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=10976&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=10976&range=00-01

  Stats: 14959 lines in 520 files changed: 6697 ins; 6140 del; 2122 mod
  Patch: https://git.openjdk.org/jdk/pull/10976.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10976/head:pull/10976

PR: https://git.openjdk.org/jdk/pull/10976