RFR: 8359808: JavaRuntimeURLConnection should only connect to non-directory resources [v4]

[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 three additional commits since the last revision:

 - Remove redundant fast-path check.
 - Change method name.
 - Feedback changes (maybe some still to be done).

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/25871/files
  - new: https://git.openjdk.org/jdk/pull/25871/files/930aa2c6..2dcfd102

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=25871&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=25871&range=02-03

  Stats: 16 lines in 2 files changed: 4 ins; 3 del; 9 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