RFR: 8339131: Remove rarely-used accessor methods from Opcode [v2]

[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.

Chen Liang has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains eight commits:

 - Revert back to enum switch, fix compile error
 - 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
 - Merge branch 'master' of https://github.com/openjdk/jdk into fix/opcode-clean
 - 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

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Changes: https://git.openjdk.org/jdk/pull/20757/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20757&range=01
  Stats: 469 lines in 8 files changed: 189 ins; 77 del; 203 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