java/eclipse: fix build consumer devel/subversive, commit files ignored with .gitignore

- Return file Makefile.plugins required for consumer devel/subversive.
- Update java version in Makefile.plugins from 8 to 17 - eclipse require
  at least 17.

- Thanks to .gitignore with line "*.sw[p-z]":
    $ git add java/eclipse/files/addons/eclipse.platform.swt
    The following paths are ignored by one of your .gitignore files:
    java/eclipse/files/addons/eclipse.platform.swt
    hint: Use -f if you really want to add them.
    hint: Disable this message with "git config advice.addIgnoredFile false"
  Force add this directory.

PR:		281123
Reported by:	yasu (email), antoine (email), Norbert Grundmann
Approved by:	Norbert Grundmann <ngrundmann@gmx.de> (maintainer)
Fixes:		27eb99fc (Update 4.24 → 4.32, take maintainership)