[code-reflection] Integrated: Hat cleanup codegen

[Gary Frost]

We have multiple tiers of c99 code gen.  

In this cleanup I moved common functionality down the class hierarchy as much as possible, to avoid duplications. 

Also preferring not to pass strings, but compuse using Core.Op and Java.Op types. 

I also separated out calls to identifer() to varName(), funcName(), keyword() ....

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Commit messages:
 - moved common code gen methods to base builder classes
 - move some code to OpTk and push some down to common HATBuilder

Changes: https://git.openjdk.org/babylon/pull/552/files
  Webrev: https://webrevs.openjdk.org/?repo=babylon&pr=552&range=00
  Stats: 508 lines in 12 files changed: 165 ins; 236 del; 107 mod
  Patch: https://git.openjdk.org/babylon/pull/552.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/552/head:pull/552

PR: https://git.openjdk.org/babylon/pull/552