[foreign-jextract] RFR: jextract thin tool, maximum api - initial refactoring

[Athijegannathan Sundararajan]

Except for Main, option handling and tool error message resoures, all moved to exposed to exported package.

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Commit messages:
 - jextract thin tool, maximum api - initial refactoring

Changes: https://git.openjdk.java.net/panama-foreign/pull/251/files
 Webrev: https://webrevs.openjdk.java.net/panama-foreign/251/webrev.00
  Stats: 1884 lines in 16 files changed: 936 ins; 940 del; 8 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/251.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/251/head:pull/251

PR: https://git.openjdk.java.net/panama-foreign/pull/251