[lworld] RFR: 8378767: [lworld] Rename Makefile functions and variables related to preview mode [v2]

[David Beaumont]

> Renames value class related functions and variables in Makefiles to reflect the more general use for preview mode classes/resources (where appropriate).
> 
> As preview mode is enabled in mainline builds, it will no longer be limited to value classes and their semantics.
> 
> After this change, the work "value" appears only once in the modified files (outside of comments) when defining GENERATED_PREVIEW_SUBDIRS.
> 
> This does change the `_the.$(MODULE).valueclasses` target to be `_the.$(MODULE).preview` but that should not be an issue.

David Beaumont has updated the pull request incrementally with one additional commit since the last revision:

  typo fix

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

Changes:
  - all: https://git.openjdk.org/valhalla/pull/2175/files
  - new: https://git.openjdk.org/valhalla/pull/2175/files/7fe92a55..24d7895d

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=valhalla&pr=2175&range=01
 - incr: https://webrevs.openjdk.org/?repo=valhalla&pr=2175&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/valhalla/pull/2175.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/2175/head:pull/2175

PR: https://git.openjdk.org/valhalla/pull/2175