RFR: 8292153: x86: Represent Registers as values [v2]

[Vladimir Ivanov]

> As of now, Registers of all sorts use pointer-based representation. It's error-prone, because compilers perform implicit conversions between pointers and integral values. Also, it constraints `MacroAssembler` API where it may introduce ambiguity between overloads.
> 
> Proposed change hides pointer representation behind value class.
> 
> Pointer-based representation is kept to avoid massive migration of users (from `->` to `.`) and to enable incremental migration on per-platform basis (pointer-based representation is assumed in shared code).
> 
> Code quality doesn't suffer (and even slightly improves):
>   https://godbolt.org/z/d8dGM1eY1
> 
> (I noticed one downside: slowdebug builds become slower, because `operator->` isn't inlined there. If it becomes a problem, migrating performance-sensitive places from `->` to `.` should solve the problem.)
> 
> Testing: hs-tier1 - hs-tier5
> 
> PS: a number of cleanups are incorporated. In particular, I decided to expand all macros from `register.hpp` because IMO they add confusion rather than improve readability.

Vladimir Ivanov has updated the pull request incrementally with one additional commit since the last revision:

  cleanups

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/9815/files
  - new: https://git.openjdk.org/jdk/pull/9815/files/4cb98cbd..478d4bed

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=9815&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=9815&range=00-01

  Stats: 33 lines in 2 files changed: 1 ins; 16 del; 16 mod
  Patch: https://git.openjdk.org/jdk/pull/9815.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9815/head:pull/9815

PR: https://git.openjdk.org/jdk/pull/9815