RFR: 8356645: Javac should utilize new ZIP file system read-only access mode [v3]

[David Beaumont]

> 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.

David Beaumont has updated the pull request incrementally with one additional commit since the last revision:

  Some (not all) feedback addressed. Still open questions.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/25639/files
  - new: https://git.openjdk.org/jdk/pull/25639/files/bc2f5232..a18a12d3

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=25639&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=25639&range=01-02

  Stats: 16 lines in 4 files changed: 5 ins; 6 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/25639.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25639/head:pull/25639

PR: https://git.openjdk.org/jdk/pull/25639