RFR: 8372617: Save and restore stubgen stubs when using an AOT code cache [v4]

[Andrew Dinn]

> This PR adds save and restore of all generated stubs to the AOT code cache on x86 and aarch64. Other arches are modified to deal with the related generic PAI changes.
> 
> Small changes were required to the aarch64 and x86_64 generator code in order to meet two key constraints:
> 1. the first declared entry of every stub starts at the first instruction in the stub code range
> 2. all data/code cross-references from one stub to another target a declared stub entry

Andrew Dinn has updated the pull request incrementally with two additional commits since the last revision:

 - fix whitespace issue
 - remaining asmehra feedback

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/28433/files
  - new: https://git.openjdk.org/jdk/pull/28433/files/ed8d2455..83855bef

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=28433&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=28433&range=02-03

  Stats: 30 lines in 7 files changed: 10 ins; 10 del; 10 mod
  Patch: https://git.openjdk.org/jdk/pull/28433.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28433/head:pull/28433

PR: https://git.openjdk.org/jdk/pull/28433