RFR: 7903271: Add sample of libzstd [v2]

[Per Minborg]

> This PR adds a sample using `libzstd`, a high-performance compression library.

Per Minborg has updated the pull request incrementally with one additional commit since the last revision:

  Simplify compile

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Changes:
  - all: https://git.openjdk.org/jextract/pull/66/files
  - new: https://git.openjdk.org/jextract/pull/66/files/4aae1ab3..1b1e3bc7

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jextract&pr=66&range=01
 - incr: https://webrevs.openjdk.org/?repo=jextract&pr=66&range=00-01

  Stats: 3 lines in 2 files changed: 0 ins; 2 del; 1 mod
  Patch: https://git.openjdk.org/jextract/pull/66.diff
  Fetch: git fetch https://git.openjdk.org/jextract pull/66/head:pull/66

PR: https://git.openjdk.org/jextract/pull/66