RFR: 8339131: Remove rarely-used accessor methods from Opcode

[Chen Liang]

In offline discussion, we agreed that current fields of `Opcode` violate data oriented design to a large extent. The attributes not generic to all opcode are removed.

Up for preliminary review; needs to be reworked for #20737.

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Commit messages:
 - Fix ofArgument in loadConstant patch instead, improve specs
 - Merge branch 'master' of https://github.com/openjdk/jdk into fix/opcode-clean
 - Merge branch 'master' of https://github.com/openjdk/jdk into fix/opcode-clean
 - Clean up opcode fields

Changes: https://git.openjdk.org/jdk/pull/20757/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20757&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8339131
  Stats: 473 lines in 8 files changed: 190 ins; 79 del; 204 mod
  Patch: https://git.openjdk.org/jdk/pull/20757.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20757/head:pull/20757

PR: https://git.openjdk.org/jdk/pull/20757