[code-reflection] RFR: Bytecode locals compaction [v2]

[Adam Sotona]

> `LocalsCompactor` is a bytecode transformation reducing generated method `maxLocals` by re-using local slots.
> Roundtrip of lift and bytecode generation doubles the `maxLocals` value, while `LocalsCompactor` reduces the regression by 50%.
> 
> Lifting of compacted locals revealed bugs in `LocalsTypeMapper` variables graph construction. This patch includes significantly  refactored `LocalsTypeMapper` to support lifting of compacted locals.
> 
> `BytecodeGenerator` has slightly improved performance (so `TestSmallCorpus` finishes in a reasonable time). However performance has not been main focus of this PR.
> 
> `TestSmallCorpus` has been slightly refactored to provide better debugging feedback and compaction statistics. Overall stability is still >99%.
> 
> Please review.
> 
> Thanks,
> Adam

Adam Sotona has updated the pull request incrementally with one additional commit since the last revision:

  added comments

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Changes:
  - all: https://git.openjdk.org/babylon/pull/224/files
  - new: https://git.openjdk.org/babylon/pull/224/files/d4c0b594..6f71c8ed

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=babylon&pr=224&range=01
 - incr: https://webrevs.openjdk.org/?repo=babylon&pr=224&range=00-01

  Stats: 6 lines in 2 files changed: 1 ins; 0 del; 5 mod
  Patch: https://git.openjdk.org/babylon/pull/224.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/224/head:pull/224

PR: https://git.openjdk.org/babylon/pull/224