[code-reflection] RFR: Replace opField with opMethod for identified methods [v3]

[Mourad Abbay]

> In this PR, instead of creating a field that will holds the textual representation of an identified method, we create a method (let's call it opMethod) that will returns the op of that method.

Mourad Abbay has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains four additional commits since the last revision:

 - Change the name of the opMethod
 - Merge branch 'code-reflection' into opMethod
 - Apply suggestions
 - Replace opField with opMethod for identified methods

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Changes:
  - all: https://git.openjdk.org/babylon/pull/299/files
  - new: https://git.openjdk.org/babylon/pull/299/files/96e02596..b198cda9

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=babylon&pr=299&range=02
 - incr: https://webrevs.openjdk.org/?repo=babylon&pr=299&range=01-02

  Stats: 10943 lines in 188 files changed: 6927 ins; 3158 del; 858 mod
  Patch: https://git.openjdk.org/babylon/pull/299.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/299/head:pull/299

PR: https://git.openjdk.org/babylon/pull/299