[code-reflection] RFR: Code transformer [v2]

[Paul Sandoz]

> Rename `OpTransformer` to `CodeTransformer`, and `CopyContext` to `CodeContext`.
> 
> Add a simplified operation transformer which is composed into a code transformer, for cases where operations are mostly replaced with one or more other operations (replacing with zero other operations is also possible). In such cases it is not necessary to deal with the code context and value mappings, nor return the block builder, as is required with a code transformer.

Paul Sandoz has updated the pull request incrementally with one additional commit since the last revision:

  Rename OpTransformerRename to OpTransformer.
  
  Update docs.

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Changes:
  - all: https://git.openjdk.org/babylon/pull/690/files
  - new: https://git.openjdk.org/babylon/pull/690/files/eb3d7b39..6315fe52

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=babylon&pr=690&range=01
 - incr: https://webrevs.openjdk.org/?repo=babylon&pr=690&range=00-01

  Stats: 20 lines in 1 file changed: 4 ins; 2 del; 14 mod
  Patch: https://git.openjdk.org/babylon/pull/690.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/690/head:pull/690

PR: https://git.openjdk.org/babylon/pull/690