RFR: 8336275: Move common Method and Constructor fields to Executable [v2]

[Chen Liang]

> Move fields common to Method and Field to executable, which simplifies implementation. Removed useless transient modifiers as Method and Field were never serializable.

Chen Liang has updated the pull request incrementally with one additional commit since the last revision:

  Redundant transient; Update the comments to be more accurate

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Changes:
  - all: https://git.openjdk.org/jdk/pull/20188/files
  - new: https://git.openjdk.org/jdk/pull/20188/files/dbe59a5f..184e8a4e

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=20188&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=20188&range=00-01

  Stats: 3 lines in 3 files changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/20188.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20188/head:pull/20188

PR: https://git.openjdk.org/jdk/pull/20188