RFR: 8350880: (zipfs) Add support for read-only zip file systems [v7]

[David Beaumont]

> Adding read-only support to ZipFileSystem.
> 
> The new `accessMode` environment property allows for readOnly and readWrite values, and ensures that the requested mode is consistent with what's returned.
> 
> This involved a little refactoring to ensure that "read only" state was set initially and only unset at the end of initialization if appropriate.
> 
> By making 2 methods return values (rather than silently set non-final fields as a side effect) it's now clear in what order fields are initialized and which are final (sadly there are still non-final fields, but only a split of this class into two types can fix that, since determining multi-jar support requires reading the file system).

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

  Changes based on feedback

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/25178/files
  - new: https://git.openjdk.org/jdk/pull/25178/files/ea781c16..46b19106

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=25178&range=06
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=25178&range=05-06

  Stats: 26 lines in 5 files changed: 6 ins; 1 del; 19 mod
  Patch: https://git.openjdk.org/jdk/pull/25178.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25178/head:pull/25178

PR: https://git.openjdk.org/jdk/pull/25178