RFR: 7903636: update jextract sample scripts for --source option removal [v3]

[Athijegannathan Sundararajan]

> * removing --source option in scripts
> * removing binary .class generating scripts (as normal scripts do compilation by javac anyway)
> * removing unnecessary --enable-preview option in run scripts.
> * updating gradle version to be the latest (8.5) so that we can use JDK 21 for gradle run itself.

Athijegannathan Sundararajan has updated the pull request incrementally with one additional commit since the last revision:

  addressed review comments.

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Changes:
  - all: https://git.openjdk.org/jextract/pull/189/files
  - new: https://git.openjdk.org/jextract/pull/189/files/796349dc..37f0d648

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jextract&pr=189&range=02
 - incr: https://webrevs.openjdk.org/?repo=jextract&pr=189&range=01-02

  Stats: 2 lines in 2 files changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jextract/pull/189.diff
  Fetch: git fetch https://git.openjdk.org/jextract.git pull/189/head:pull/189

PR: https://git.openjdk.org/jextract/pull/189