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 pull request now contains 12 commits:

 - Merge branch 'jdk_8368467_reader/squashed' into jdk_8368475_makefile/squashed
 - Rollup of makefile change and jlink fix (temp).
   
   * likely test fix
   * Copy value classes into preview directories for inclusion in jimage
 - [[AUTOMATIC FORMATTING]]
 - fixing tests after refactoring
 - Fixing up after dependent PR changes
 - feedback and remove unused code
 - [[AUTOMATIC FORMATTING]]
 - new tests for ImageLocation
 - Restoring lost changes and updating some comments.
 - add system property guard to preview mode
 - ... and 2 more: https://git.openjdk.org/valhalla/compare/1cc77d40...747b24d0

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Changes: https://git.openjdk.org/valhalla/pull/1719/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1719&range=01
  Stats: 1543 lines in 28 files changed: 414 ins; 236 del; 893 mod
  Patch: https://git.openjdk.org/valhalla/pull/1719.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1719/head:pull/1719

PR: https://git.openjdk.org/valhalla/pull/1719