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

[David Beaumont]

Copies valuetype classes for each module into corresponding "/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".

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Commit messages:
 - Copy value classes into preview directories for inclusion in jimage

Changes: https://git.openjdk.org/valhalla/pull/1727/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1727&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8368475
  Stats: 22 lines in 1 file changed: 20 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/valhalla/pull/1727.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1727/head:pull/1727

PR: https://git.openjdk.org/valhalla/pull/1727