[code-reflection] RFR: Lambda model uniqueness [v6]

[Mourad Abbay]

> Lambdas that share the same proxy class, have the same implementation and therefore have the same code model generated by the compiler. In this PR, we share the code model across instances of the same proxy class. 
> This also means we reduce execution time as we only need to invoke `opMethod` once for given proxy class.
> With these changes we can compare lambda code model based on identity.

Mourad Abbay has refreshed the contents of this pull request, and previous commits have been removed. The incremental views will show differences compared to the previous content of the PR. The pull request contains one new commit since the last revision:

  Apply Paul's comments

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Changes:
  - all: https://git.openjdk.org/babylon/pull/420/files
  - new: https://git.openjdk.org/babylon/pull/420/files/849aa6e6..ade697ba

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=babylon&pr=420&range=05
 - incr: https://webrevs.openjdk.org/?repo=babylon&pr=420&range=04-05

  Stats: 146 lines in 1 file changed: 61 ins; 80 del; 5 mod
  Patch: https://git.openjdk.org/babylon/pull/420.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/420/head:pull/420

PR: https://git.openjdk.org/babylon/pull/420