RFR: 7903933: Move sharable items from different generations to a common file [v4]

[Nizar Benalla]

> Please review this patch to move the `C_*` layouts and the static utility methods into separate classes: `LayoutUtils.java` and `FFMUtils.java`, respectively.
> 
> - The names could later be personalized through a JSON configuration.
> - We can use static imports if the `-t` option is no used and the files are generated into the default package, in that case we use the classname to call the static methods or use the `C_*` constants.
> 
> Some tests had to be modified slightly, either by adding new static imports or replacing classnames.

Nizar Benalla 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 six additional commits since the last revision:

 - Merge branch 'master' into shareable-items
 - add new option to create a sharable utility class
   
   cleanup: longer cmd option `framework` should use -- rather than -
   
   small other cleanups
 - Merge branch 'master' into shareable-items
 - Revert all changes - starting over from scratch
 - replace hardcoded strings I missed
 - move sharable items to a common class

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

Changes:
  - all: https://git.openjdk.org/jextract/pull/278/files
  - new: https://git.openjdk.org/jextract/pull/278/files/736ccfba..69d46473

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jextract&pr=278&range=03
 - incr: https://webrevs.openjdk.org/?repo=jextract&pr=278&range=02-03

  Stats: 2 lines in 2 files changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jextract/pull/278.diff
  Fetch: git fetch https://git.openjdk.org/jextract.git pull/278/head:pull/278

PR: https://git.openjdk.org/jextract/pull/278