RFR: 8329332: Remove CompiledMethod and CodeBlobLayout classes [v2]

[Vladimir Kozlov]

> Revert [JDK-8152664](https://bugs.openjdk.org/browse/JDK-8152664) RFE [changes](https://github.com/openjdk/jdk/commit/b853eb7f5ca24eeeda18acbb14287f706499c365) which was used for AOT [JEP 295](https://openjdk.org/jeps/295) implementation in JDK 9. The code was left in HotSpot assuming it will help in a future. But during work on Leyden we decided to not use it. In Leyden cached compiled code will be restored in CodeCache as normal nmethods: no need to change VM's runtime and GC code to process them.
> 
> I may work on optimizing `CodeBlob` and `nmethod` fields layout to reduce header size in separate changes. In these changes I did simple fields reordering to keep small (1 byte) fields together.
> 
> I do not see (and not expected) performance difference with these changes.
> 
> Tested tier1-5, xcomp, stress. Running performance testing.
> 
> I need help with testing on platforms which Oracle does not support.

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

  Removed not_used state of nmethod

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/18554/files
  - new: https://git.openjdk.org/jdk/pull/18554/files/7635b333..246ff68a

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=18554&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=18554&range=00-01

  Stats: 5 lines in 2 files changed: 0 ins; 3 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/18554.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18554/head:pull/18554

PR: https://git.openjdk.org/jdk/pull/18554