Dropping java 11 support

[MartinWitt]

As JDT moved to java 17 #5268 we also need to move. Our current migration plan is to make the 10.4 release soon, when the CD script works. Then we start working on the java 20/21 features on a different branch. On this branch, we also start the cleanup we need to do while dropping java 11. Then there will be a last spoon release with 10.5(?). Merging the java20/21 branch will result in the first spoon release for JDK 17+. Spoon can still analyze older source code. As a user, you only need a newer java version. There will be no back porting of fixes to older java 11 releases.

[monperrus]

OK with the plan, we are married to JDT anyway.

[MartinWitt]

Next step is to create a branch called java17 which is a valid PR target for the meantime. We will start working there for all the changes we need to do for this switch. I also created a label for these PRs/Issues.

Branch: https://github.com/INRIA/spoon/tree/java17

[MartinWitt]

Java 11 support is now dropped in the latest Spoon 11 release.