RFR: 8316851: Add @sealedGraph to Executable

[Per Minborg]

This PR proposes to add the @sealedGraph tag to `java.lang.reflect.Executable`.

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Commit messages:
 - Add @SealedGraph to Executable

Changes: https://git.openjdk.org/jdk/pull/15897/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15897&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8316851
  Stats: 1 line in 1 file changed: 1 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/15897.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15897/head:pull/15897

PR: https://git.openjdk.org/jdk/pull/15897