[code-reflection] Integrated: More bld simplifications. Prep for adding jextract

[Gary Frost]

Preparing for addition of jextract to bld and mkpoms. 

Mostly bld cleanup and additional .gitignores

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Commit messages:
 - More bld simplifications.  Prep for adding jextract

Changes: https://git.openjdk.org/babylon/pull/286/files
  Webrev: https://webrevs.openjdk.org/?repo=babylon&pr=286&range=00
  Stats: 334 lines in 19 files changed: 70 ins; 67 del; 197 mod
  Patch: https://git.openjdk.org/babylon/pull/286.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/286/head:pull/286

PR: https://git.openjdk.org/babylon/pull/286