[foreign-jextract] RFR: 8252047: jextract generates uncompilable code with --source option

[Athijegannathan Sundararajan]

Splitting constant helper class into multiple classes.
Piggybacking to avoid generating "long double" fields, variables, arguments.

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Commit messages:
 - 8252047: jextract generates uncompilable code with --source option

Changes: https://git.openjdk.java.net/panama-foreign/pull/286/files
 Webrev: https://webrevs.openjdk.java.net/panama-foreign/286/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8252047
  Stats: 167 lines in 2 files changed: 114 ins; 4 del; 49 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/286.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/286/head:pull/286

PR: https://git.openjdk.java.net/panama-foreign/pull/286