RFR: 8342967: Lambda deduplication fails with non-metafactory BSMs and mismatched local variables names

[Aggelos Biboudis]

After experimentation and under certain conditions, a few equivalent lambdas (up to variable renaming) fail to deduplicate.

`TreeHasher` and `TreeDiffer` are now aware that other bootstraps may appear in lambda bodies (e.g. `SwitchBootstraps.typeSwitch`) and that variable names do not matter (when they appear in method/lambda definitions). In the first case equivalence is checked based on `bsmKey` and not the `Dynamic{Var, Method}Symbol` itself.

The test was also adjusted since it was assuming BSM with certain structure only (that `.get(1)` was unprotected).

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Commit messages:
 - 8342967: Lambda deduplication fails with non-metafactory BSMs and mismatched local variables names

Changes: https://git.openjdk.org/jdk/pull/21687/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21687&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8342967
  Stats: 89 lines in 6 files changed: 63 ins; 2 del; 24 mod
  Patch: https://git.openjdk.org/jdk/pull/21687.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21687/head:pull/21687

PR: https://git.openjdk.org/jdk/pull/21687