[foreign-jextract] RFR: 8240602: port more tests from old jextract tests

[Athijegannathan Sundararajan]

* catch RuntimeException around header parser and return failure exit code.
* add union, (macro) constants and bad bitfield tests.
* IDE suggested simplyfing refactorings

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Commits:
 - 0228346a: tab removal in comments (jcheck failure)
 - 2e7fddc0: 8240602: port more tests from old jextract tests

Changes: https://git.openjdk.java.net/panama-foreign/pull/39/files
 Webrev: https://webrevs.openjdk.java.net/panama-foreign/39/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8240602
  Stats: 441 lines in 10 files changed: 421 ins; 3 del; 17 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/39.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/39/head:pull/39

PR: https://git.openjdk.java.net/panama-foreign/pull/39