[code-reflection] RFR: Enhance grammar of op attributes [v2]

[Maurizio Cimadamore]

> This PR enhances the grammar of op attributes, so as to avoid use of "stringy" attributes where possible. Now all attributes that are Java primitives are externalized and re-parsed back automatically. This means that op factories no longer need to test for attribute values of type `String` and then manually parse that string back into the correct primitive, which makes the code more robust.
> 
> This change caused some reshuffling in the tests -- most notably, when fixing the triton test, the new logic highlighted what was probably an "issue" in the triton transformer (see related comment).

Maurizio Cimadamore has updated the pull request incrementally with one additional commit since the last revision:

  Simplify code and add comment

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Changes:
  - all: https://git.openjdk.org/babylon/pull/435/files
  - new: https://git.openjdk.org/babylon/pull/435/files/3db61a94..b3139a49

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=babylon&pr=435&range=01
 - incr: https://webrevs.openjdk.org/?repo=babylon&pr=435&range=00-01

  Stats: 5 lines in 1 file changed: 3 ins; 2 del; 0 mod
  Patch: https://git.openjdk.org/babylon/pull/435.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/435/head:pull/435

PR: https://git.openjdk.org/babylon/pull/435