RFR: 7903630: jextract emits duplicate symbols for macro clashing with enum constants [v2]

[Maurizio Cimadamore]

> The removal of `EnumConstantLifter` caused certain name conflicts to go undetected by `DuplicateFilter`. More specifically, if a macro constant has same name as that of an enum constant, given the enum constant is no longer lifted to toplevel, `DuplicateFilter` will not see the clash. The fix is to tweak `DuplicateFilter` to recurse into enums.

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

  Add extra test case

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Changes:
  - all: https://git.openjdk.org/jextract/pull/177/files
  - new: https://git.openjdk.org/jextract/pull/177/files/69e3bce8..a782c5d0

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jextract&pr=177&range=01
 - incr: https://webrevs.openjdk.org/?repo=jextract&pr=177&range=00-01

  Stats: 2 lines in 2 files changed: 2 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jextract/pull/177.diff
  Fetch: git fetch https://git.openjdk.org/jextract.git pull/177/head:pull/177

PR: https://git.openjdk.org/jextract/pull/177