RFR: [lworld] Switch JLink to not use ImageReader API [v4]

[David Beaumont]

> Creates a new, narrowed API explicitly for use by jlink, which view the resource entries in a jimage file without the re-mapping of names and invention of synthetic entries inherent in ImageReader.
> 
> Another good reason to express this new API as something other than ImageReader is that, to fix issues such as [JDK-8357249](https://bugs.openjdk.org/browse/JDK-8357249), we don't want to have the (System)ImageReader class used directly in jlink code. It's just the wrong abstraction and will make it harder to refactor jlink to use a non-singleton API with a controlled lifetime later. 
> 
> I've not added unit tests for the new API (yet), but the fact the PackagedModulesVsRuntimeImageLinkTest passes with preview content in the jimage file means that it's working as expected.

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

  Added copyright notice and tidied a couple of comments.

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Changes:
  - all: https://git.openjdk.org/valhalla/pull/1721/files
  - new: https://git.openjdk.org/valhalla/pull/1721/files/67984e27..a2f0c0c9

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=valhalla&pr=1721&range=03
 - incr: https://webrevs.openjdk.org/?repo=valhalla&pr=1721&range=02-03

  Stats: 32 lines in 2 files changed: 30 ins; 1 del; 1 mod
  Patch: https://git.openjdk.org/valhalla/pull/1721.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1721/head:pull/1721

PR: https://git.openjdk.org/valhalla/pull/1721