[lworld] RFR: 8368475: [lworld] Add preview classes to jimage at make time

[David Beaumont]

Copies valuetype classes for each module into corresponding "<module>/META-INF/preview/..." sub-directories to be pulled into jimage files and processed by the new preview mode handling code.

There might be a better way to do this in terms of Makefile semantics, but this seems to work well enough and doesn't prevent the value-class JAR files being generated for patching (which is still how everyone will get value classes until the rest of the work is plumbed in).

To enable the new preview mode work, set the "DISABLE_PREVIEW_PATCHING" system property to "true".

This PR is stacked on top of https://github.com/openjdk/valhalla/pull/1615 and only contains the single commit:
https://github.com/openjdk/valhalla/commit/d5941080fc1983fd436fc60962630f27b561a9b3

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Commit messages:
 - Copy value classes into preview directories for inclusion in jimage
 - [[AUTOMATIC FORMATTING]]
 - Remove TODOs now jimage version is bumped
 - jimage writer changes to support preview mode.
 - Word smithing flags definitions.
 - [[AUTOMATIC FORMATTING]]
 - 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

Changes: https://git.openjdk.org/valhalla/pull/1616/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1616&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8368475
  Stats: 3822 lines in 35 files changed: 2103 ins; 388 del; 1331 mod
  Patch: https://git.openjdk.org/valhalla/pull/1616.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1616/head:pull/1616

PR: https://git.openjdk.org/valhalla/pull/1616