RFR: 8356645: Javac should utilize new ZIP file system read-only access mode

[Jan Lahoda]

On Wed, 4 Jun 2025 12:08:38 GMT, David Beaumont <duke at openjdk.org> wrote:

> This PR seeks to integrate the new ZipFileSystem "accessMode" parameter to open internal ZIP/JAR files as read only, to act as defense in-depth against accidental modification.
> 
> Note that this currently also propagates the (currently undocumented) "zipinfo-time" parameter to several other places where ZIP/JAR files are opened, which is likely to improve performance. This was discussed and is expected to be safe (but it's something to be careful about).
> This will, of course, be thoroughly tested before integration.
> 
> It also unifies several places to use a common helper method to obtain the environment map, adds more comments, and changes a small number of affected tests.
> 
> I'm also happy to update the original bug description to include the timestamp related changes as necessary.

Overall seems like a reasonable direction. Please see some comments inline.

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PR Review: https://git.openjdk.org/jdk/pull/25639#pullrequestreview-2915722091