RFR: 8372617: Save and restore stubgen stubs when using an AOT code cache [v16]

[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 with a new target base due to a merge or a rebase. The pull request now contains 49 commits:

 - merge
 - add AOT logging for C strings
 - fix PrintStubs when loading AOT stubs
 - add missing ZGC external
 - add missing reloc for some stub calls
 - fix klass encode/decode for AOT code
 - merge
 - ensure C1 treats ThreadIdentifier::unsafe_offset() as an external address
 - configure low heap size to exercise more stub code
 - Run AOTCodeFlags test with multiple GCs
 - ... and 39 more: https://git.openjdk.org/jdk/compare/ae4df28b...96c30b31

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Changes: https://git.openjdk.org/jdk/pull/28433/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28433&range=15
  Stats: 5704 lines in 63 files changed: 4663 ins; 444 del; 597 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