RFR: 8359808: JavaRuntimeURLConnection should only connect to non-directory resources [v3]

[David Beaumont]

> Simplifying JavaRuntimeURLConnection to avoid accidentally returning non-resource data to users.
> 
> This change has the following distinct parts:
> 1. Refactor code to use Node instead of directly accessing low level ImageLocation type.
> 2. Remove unnecessary use of "Resource" interface and related URL generation code (completely unreachable).
> 3. Adding comments explaining why there's a non-obvious distinction in how module and resource names are treated with respect to URL percent encoding.
> 4. Small constructor logic simplification (module name cannot be null anymore)
> 5. Small simplification around 'READER' use, since it is impossible for that to ever be null (other users of ImageReaderFactory already assume it could never be null, and code path analysis agrees).
> 6. Adding tests for the non-resource cases.
> 7. Adding extra test data to check the behaviour with respect to things like percent escaping (previously untested).
> 8. Adding TODO comments for things I could do in this PR or later (reviewer opinions welcome).

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

  Feedback changes and renaming field to match nomenclature of JEP 220.

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/25871/files
  - new: https://git.openjdk.org/jdk/pull/25871/files/3bafc256..930aa2c6

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=25871&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=25871&range=01-02

  Stats: 27 lines in 1 file changed: 2 ins; 11 del; 14 mod
  Patch: https://git.openjdk.org/jdk/pull/25871.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25871/head:pull/25871

PR: https://git.openjdk.org/jdk/pull/25871