[code-reflection] RFR: Support storing the code that builds the code model [v6]

[Mourad Abbay]

> In this PR we allow the user to decide how to store the code model. The first option is `TEXT`, if this is selected, we store the textual representation of the code model. The second option is `CODE_BUILDR`, if this is selected, we store the code that builds the code model. All work done here is around the second option, because the first option is already supported.

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

 - Reformat code
 - Apply fixes from Maurizio

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Changes:
  - all: https://git.openjdk.org/babylon/pull/305/files
  - new: https://git.openjdk.org/babylon/pull/305/files/16b16087..21c12cb3

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=babylon&pr=305&range=05
 - incr: https://webrevs.openjdk.org/?repo=babylon&pr=305&range=04-05

  Stats: 16 lines in 1 file changed: 2 ins; 6 del; 8 mod
  Patch: https://git.openjdk.org/babylon/pull/305.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/305/head:pull/305

PR: https://git.openjdk.org/babylon/pull/305