[code-reflection] RFR: Replace opField with opMethod for identified methods [v2]

[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 incrementally with one additional commit since the last revision:

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Changes:
  - all: https://git.openjdk.org/babylon/pull/299/files
  - new: https://git.openjdk.org/babylon/pull/299/files/93581b2a..96e02596

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=babylon&pr=299&range=01
 - incr: https://webrevs.openjdk.org/?repo=babylon&pr=299&range=00-01

  Stats: 41 lines in 5 files changed: 11 ins; 20 del; 10 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