[lworld] RFR: 8368475: [lworld] Add preview classes to jimage at make time [v2]

[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".

David Beaumont has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains three additional commits since the last revision:

 - rename marker, tweak comments
 - Merge branch 'lworld' into jdk_8368475_makefile/squashed
 - Copy value classes into preview directories for inclusion in jimage

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

Changes:
  - all: https://git.openjdk.org/valhalla/pull/1727/files
  - new: https://git.openjdk.org/valhalla/pull/1727/files/e38847af..09327056

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=valhalla&pr=1727&range=01
 - incr: https://webrevs.openjdk.org/?repo=valhalla&pr=1727&range=00-01

  Stats: 19533 lines in 544 files changed: 10949 ins; 5453 del; 3131 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