[lworld] RFR: 8368333: [lworld] Add preview mode to ImageReader and JRT file-system [v4]

[David Beaumont]

> Java changes for supporting preview mode when preview mode resources (with new location flags) are available.
> 
> At the moment, this code will operate on non-preview jimage files (1.0) and act as if no preview resources are available by virtue of the default value for missing attributes and package flags being zero (which matches jimage 1.0).
> 
> Compare and review this against https://github.com/openjdk/valhalla/pull/1609.
> 
> https://github.com/openjdk/valhalla/pull/1613/files/4e21d5e00ac05d4197e8c617dbabec84ce8748f9..a55450f04523454c489caa67db0fb5d7b6cb80c2

David Beaumont has refreshed the contents of this pull request, and previous commits have been removed. The incremental views will show differences compared to the previous content of the PR. The pull request contains five new commits since the last revision:

 - Word smithing flags definitions.
 - Add workaround until new image writing code is in
 - Clarifying flag docs for /packages/xxx case
 - Java ImageReader changes for preview mode
 - C++ preparation for preview mode

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Changes:
  - all: https://git.openjdk.org/valhalla/pull/1613/files
  - new: https://git.openjdk.org/valhalla/pull/1613/files/a55450f0..629ba8cc

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=valhalla&pr=1613&range=03
 - incr: https://webrevs.openjdk.org/?repo=valhalla&pr=1613&range=02-03

  Stats: 0 lines in 0 files changed: 0 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/valhalla/pull/1613.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1613/head:pull/1613

PR: https://git.openjdk.org/valhalla/pull/1613