RFR: 8336275: Move common Method and Constructor fields to Executable

[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.

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Commit messages:
 - Inline some common ctor + method fields to executable

Changes: https://git.openjdk.org/jdk/pull/20188/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20188&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8336275
  Stats: 451 lines in 11 files changed: 77 ins; 238 del; 136 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