[code-reflection] RFR: Model String Template [v6]

[Mourad Abbay]

> Model String Template

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

 - Simplify variables names inside visitStringTemplate
 - Refactor StringTemplateOp.resultType() to give clear errors
 - Add a test for String Template
 - Revert VarOp to its original form

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Changes:
  - all: https://git.openjdk.org/babylon/pull/30/files
  - new: https://git.openjdk.org/babylon/pull/30/files/7c3fe6cb..e0e09e8e

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=babylon&pr=30&range=05
 - incr: https://webrevs.openjdk.org/?repo=babylon&pr=30&range=04-05

  Stats: 110 lines in 5 files changed: 44 ins; 46 del; 20 mod
  Patch: https://git.openjdk.org/babylon/pull/30.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/30/head:pull/30

PR: https://git.openjdk.org/babylon/pull/30