[foreign-jextract] RFR: adding tensorflow sample

[Athijegannathan Sundararajan]

Adding a simple tensorflow sample that uses tensorflow C API with Panama

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Commit messages:
 - adding tensorflow sample

Changes: https://git.openjdk.java.net/panama-foreign/pull/312/files
 Webrev: https://webrevs.openjdk.java.net/?repo=panama-foreign&pr=312&range=00
  Stats: 336 lines in 2 files changed: 245 ins; 0 del; 91 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/312.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/312/head:pull/312

PR: https://git.openjdk.java.net/panama-foreign/pull/312