RFR: 8339710: Avoid initializing AccessFlag related classes in write-only cases

[Claes Redestad]

This PR reduces number of classes loaded on a minimal lambda bootstrapping test by 4 by avoiding the need to pull in some AccessFlag classes.

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Commit messages:
 - Add withFlag(int) to DFB for consistency
 - Avoid loading AccessFlag by providing overrides

Changes: https://git.openjdk.org/jdk/pull/20904/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20904&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8339710
  Stats: 33 lines in 2 files changed: 30 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/20904.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20904/head:pull/20904

PR: https://git.openjdk.org/jdk/pull/20904