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

[Maurizio Cimadamore]

On Mon, 22 Jan 2024 11:01:17 GMT, Athijegannathan Sundararajan <sundar at openjdk.org> wrote:

>> * 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.

Marked as reviewed by mcimadamore (Reviewer).

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PR Review: https://git.openjdk.org/jextract/pull/189#pullrequestreview-1836461679