update java version

[jukzi]

JDT just dropped support for java <1.8
it would be good if ECJ could update all the used java version so that it can be still be compiled with current eclipse.
See eclipse-platform/.github#220 for current compilation error.

To update java version from <1.8 to 17 a regular expression search and replace could be used:

in org.eclipse.jdt.core.prefs:

   (org.eclipse.jdt.core.compiler.codegen.targetPlatform|org.eclipse.jdt.core.compiler.compliance|org.eclipse.jdt.core.compiler.source)=.*
-> $1=17

in .classpath:

   org.eclipse.jdt.internal.debug.ui.launcher.StandardVMType/([^"]*)
-> org.eclipse.jdt.internal.debug.ui.launcher.StandardVMType/JavaSE-17

However i don't know if you want to update historic projects too - like for example doc/tutorials/EclipseCON 2009 and which bundles need a version bump. So i can provide a dump search&replace but you will probably need to adopt it to your needs.