RFR: 7903933: Move sharable items from different generations to a common file [v5]

[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 pull request now contains eight commits:

 - - Move shared symbols to a different class
   - Add option to override the name of the shared symbol class
 - Merge branch 'master' into shareable-items
 - 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

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Changes: https://git.openjdk.org/jextract/pull/278/files
  Webrev: https://webrevs.openjdk.org/?repo=jextract&pr=278&range=04
  Stats: 155 lines in 10 files changed: 107 ins; 19 del; 29 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