RFR: 8317868: Add @sealedGraph to MethodHandleDesc and descendants

[Per Minborg]

This PR proposes to add  @sealedGraph to MethodHandleDesc and descendants.

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Commit messages:
 - Add @sealedGraph to MethodHandleDesc and descendants

Changes: https://git.openjdk.org/jdk/pull/16137/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16137&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8317868
  Stats: 3 lines in 2 files changed: 2 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/16137.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16137/head:pull/16137

PR: https://git.openjdk.org/jdk/pull/16137