RFR: 8356700: Declare incompressible scope in fill_words / zero_memory assembler routines [v2]

[Anjian-Wen]

> The correctness of the logic depends on the fixed instruction size of the store instructions
> emitted by the loop in MacroAssembler::fill_words and MacroAssembler::zero_memory assembler
> routines. These store instructions won't be compressed into 16-bit format due to negative
> offset immediate. But it will be safer to make it explict by declaring an incompressible scope
> when emitting these store instructions. This also renames IncompressibleRegion to IncompressibleScope.
> 
> Tier1 tested on linux-riscv64 platforms.

Anjian-Wen has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains two additional commits since the last revision:

 - Merge branch 'openjdk:master' into declare_incompressible
 - RISCV: Declare incompressible scope in fill_words / zero_memory assembler routines

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/25172/files
  - new: https://git.openjdk.org/jdk/pull/25172/files/bf4d2c47..92a7cb54

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=25172&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=25172&range=00-01

  Stats: 7107 lines in 411 files changed: 4262 ins; 1502 del; 1343 mod
  Patch: https://git.openjdk.org/jdk/pull/25172.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25172/head:pull/25172

PR: https://git.openjdk.org/jdk/pull/25172