[code-reflection] RFR: Replace opField with opMethod for lambdas. [v2]

[Mourad Abbay]

> We replace field holding the textual representation of an identified lambda with method that returns the representation of that lambda.

Mourad Abbay has updated the pull request incrementally with two additional commits since the last revision:

 - Call ModuleLayer#findLoader once and cache the result
 - Change JCTree#codeModel 's type to MethodSymbol

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Changes:
  - all: https://git.openjdk.org/babylon/pull/301/files
  - new: https://git.openjdk.org/babylon/pull/301/files/e552d41d..5c5f8e48

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=babylon&pr=301&range=01
 - incr: https://webrevs.openjdk.org/?repo=babylon&pr=301&range=00-01

  Stats: 10 lines in 3 files changed: 0 ins; 3 del; 7 mod
  Patch: https://git.openjdk.org/babylon/pull/301.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/301/head:pull/301

PR: https://git.openjdk.org/babylon/pull/301