RFR: 7903121: initial jextract tool code, tests and samples

[Athijegannathan Sundararajan]

Adding initial standalone jextract code, tests and samples.

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Commit messages:
 - 7903121: initial jextract tool code, tests and samples
 - fixed whitespaces, tabs and executable permission.
 - initial commit

Changes: https://git.openjdk.java.net/jextract/pull/2/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jextract&pr=2&range=00
  Issue: https://bugs.openjdk.java.net/browse/CODETOOLS-7903121
  Stats: 34702 lines in 401 files changed: 34699 ins; 2 del; 1 mod
  Patch: https://git.openjdk.java.net/jextract/pull/2.diff
  Fetch: git fetch https://git.openjdk.java.net/jextract pull/2/head:pull/2

PR: https://git.openjdk.java.net/jextract/pull/2