RFR: 8343789: Move mutable nmethod data out of CodeCache [v6]

[Boris Ulasevich]

> This change relocates mutable data (such as relocations, oops, and metadata) from the nmethod. The change follows the recent PR #18984, which relocated immutable nmethod data from the CodeCache.
> 
> The core idea remains the same: use the CodeCache for executable code while moving additional data to the C heap. The primary motivations are improving security and enhancing code density.
> 
> Although performance is not the main focus, testing on AArch64 CPUs, where code density plays a significant role, has shown a 1–2% performance improvement in specific scenarios, such as the CodeCacheStress test and the Renaissance Dotty benchmark.
> 
> The numbers. Immutable data constitutes **~30%** on the nmehtod. Mutable data constitutes **~8%** of nmethod. Example (statistics collected on the CodeCacheStress benchmark):
> - nmethod_count:134000, total_compilation_time: 510460ms
> - total allocation time malloc_mutable/malloc_immutable/CodeCache_alloc: 62ms/114ms/6333ms,
> - total allocation size (mutable/immutable/nmentod): 64MB/192MB/488MB
> 
> Functional testing: jtreg on arm/aarch/x86.
> Performance testing: renaissance/dacapo/SPECjvm2008 benchmarks.
> 
> Alternative solution (see comments): In the future, relocations can be moved to _immutable_data.

Boris Ulasevich has updated the pull request incrementally with one additional commit since the last revision:

  removing dead code

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/21276/files
  - new: https://git.openjdk.org/jdk/pull/21276/files/b4c7c24b..6b97993a

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=21276&range=05
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=21276&range=04-05

  Stats: 10 lines in 1 file changed: 0 ins; 5 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/21276.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21276/head:pull/21276

PR: https://git.openjdk.org/jdk/pull/21276