[code-reflection] RFR: BytecodeLift directly calculating local variables + related BytecodeGenerator fixes [v4]

[Adam Sotona]

> Proposal of `BytecodeLift` implementation skipping intermediate use of `SlotOp` and `SlotSSA` transformation.
> `LocalsTypeMapper` already handled majority of the variable mapping and its complexity grew to cover more use cases.
> This patch adds a very simple slots model to `LocalsTypeMapper` to compute variables out of the bytecode directly .
> `BytecodeLift` now knows all necessary information to emit relevant `VarOp` and `VarAccessOp`  directly.
> 
> Stability of `TestSmallCorpus` has slightly degraded, however it is just a temporary regression.
> 
> Please review.
> 
> Thanks,
> Adam

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

  roundtrip stabilization

-------------

Changes:
  - all: https://git.openjdk.org/babylon/pull/218/files
  - new: https://git.openjdk.org/babylon/pull/218/files/eb00a7e4..240c3888

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=babylon&pr=218&range=03
 - incr: https://webrevs.openjdk.org/?repo=babylon&pr=218&range=02-03

  Stats: 24 lines in 2 files changed: 10 ins; 2 del; 12 mod
  Patch: https://git.openjdk.org/babylon/pull/218.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/218/head:pull/218

PR: https://git.openjdk.org/babylon/pull/218